Extra alignment tab has been changed to \cr for TabularX centering

Question

Problems:

Extra alignment tab has been changed to \cr.

Which I think means something like the LaTeX code has a different amount of cells in this row than what was defined in the tabularx premable.

The issue doesn't exist until I attempt to add more rows after the header, but the last cell on the right is sort of...elevated? I don't quite understand the problem here, I mean in a tabularx environment you separate cells by & and end a row by // , right?

Also, if you change the last header title to: {\centering T} it doesn't crash or elevate the text but...it doesn't center the text.

Any ideas?

NOTES: The bigger picture here is that I want to align the header differently than the cells. So I'm trying to just use \centering on the header. \begin{center} does it but puts a ton of space around it.

MWE:

\documentclass[11pt]{letter}                              
\usepackage[letterpaper, inner=18mm, outer=18mm, top=8mm, bottom=25mm]{geometry}
\usepackage{tabularx}                                               
\usepackage[table,xcdraw]{xcolor}
    
\renewcommand{\tabularxcolumn}[1]{>{\tiny}m{#1}}
\newcolumntype{x}{>{\raggedleft\arraybackslash}X}  
        
\begin{document}

    \rowcolors{1}{}{gray!15}
        \begin{tabularx}{\textwidth}{xxxxxxxxxxxx}
            \rowcolor{gray}

    \color{white}\fontsize{6pt}{6pt}\selectfont \centering Text  &          
    \color{white}\fontsize{6pt}{6pt}\selectfont \centering text &   
    \color{white}\fontsize{6pt}{6pt}\selectfont \centering Text &   
    \color{white}\fontsize{6pt}{6pt}\selectfont \centering Text  &  
    \color{white}\fontsize{6pt}{6pt}\selectfont \centering Text &   
    \color{white}\fontsize{6pt}{6pt}\selectfont \centering Text  &  
    \color{white}\fontsize{6pt}{6pt}\selectfont \centering Text  &  
    \color{white}\fontsize{6pt}{6pt}\selectfont \centering Text  &  
    \color{white}\fontsize{6pt}{6pt}\selectfont \centering Text Text Text &     
    \color{white}\fontsize{6pt}{6pt}\selectfont \centering Text  &  
    \color{white}\fontsize{6pt}{6pt}\selectfont \centering Text  &  
    \color{white}\fontsize{6pt}{6pt}\selectfont {\centering Tt} \\  

    \color{black}\fontsize{6pt}{6pt}\selectfont 8'  & 
    \color{black}\fontsize{6pt}{6pt}\selectfont 130  & 
    \color{black}\fontsize{6pt}{6pt}\selectfont 134  & 
    \color{black}\fontsize{6pt}{6pt}\selectfont 152  & 
    \color{black}\fontsize{6pt}{6pt}\selectfont 168  & 
    \color{black}\fontsize{6pt}{6pt}\selectfont 200  & 
    \color{black}\fontsize{6pt}{6pt}\selectfont 240  & 
    \color{black}\fontsize{6pt}{6pt}\selectfont 340  & 
    \color{black}\fontsize{6pt}{6pt}\selectfont 520  & 
    \color{black}\fontsize{6pt}{6pt}\selectfont 340  & 
    \color{black}\fontsize{6pt}{6pt}\selectfont 520  & 
    \color{black}\fontsize{6pt}{6pt}\selectfont -  \\

\end{tabularx}
\end{document}

Edit:

Firstly, it may seem really inconvenient how I'm repeating a lot of things but really I'm just typing it once and the computer is repeating it in a loop.

I haven't been using multicolumn because the headers extend past the table cells widths and I cannot define a static width for each cell (or I wouldn't have a problem) because in the BIGGER picture I'm templating the LaTeX file with Scriban and I'm dealing with a dynamic header. Here is what happens when using multicolumn:

I was able to center the headers with \begin{center} but the space around each header cell was undesirable, so I looked it up and tried a new environment here: How can I change the whitespace above and below center? which was able to remove the space above, but not below. I placed the \begin and \end{center} right before and after each header cell. Here is what that looks like:

I don't need tiny cells, I just thought that would change the width multicolumn forcing for the headers.

I was just puzzled because tabular is reacting weirdly to the \centering modifier in each line.

Also, I am using tabularX because it extends it dynamically to the end of the page.

Answer 1

After one year (I have obviously overlooked this issue before) ...

I would wrote your table very differently:

• font size I would define before tabularx, by this all their repetitions in each cell become superfluous
• I wonder if you really need so small fonts. From provided content of table can be concluded, that font size can be much large, for example equal to \small
• for changing align column headers contents I would define new command:

  \newcommand\mcw[1]{\multicolumn{1}{C}{\textcolor{white}{#1}}}
  

  where C is defined as >{\centering\arraybackslash}X
• I also would add small vertical spaces above cells contents by \setlength\extrarowheight{2pt}
• after those measures code for table become much shorter and clear, consequently much less prone to errors in writing it:

\documentclass[11pt]{article}%{letter}
\usepackage[letterpaper, inner=18mm, outer=18mm, top=8mm, bottom=25mm]{geometry}
\usepackage{tabularx}
\newcolumntype{L}{>{\raggedright\arraybackslash}X}
\newcolumntype{C}{>{\centering\arraybackslash}X}
\usepackage[table, xcdraw]{xcolor}
\newcommand\mcw[1]{\multicolumn{1}{C}{\textcolor{white}{#1}}}

\begin{document}
    \begin{table}[ht]
    \small\linespread{0.84}\selectfont\relax%\fontsize{6pt}{6pt}\selectfont\relax
    \setlength\extrarowheight{2pt}
    \rowcolors{1}{}{gray!15}
 \begin{tabularx}{\textwidth}{*{12}{L}}
            \rowcolor{gray}
\mcw{Text} & \mcw{Text} & \mcw{Text} & \mcw{Text} & \mcw{Text} & \mcw{Text} &
\mcw{Text Text Text} 
           & \mcw{Text} & \mcw{Text} & \mcw{Text} & \mcw{Text} & \mcw{Tt}       \\
%
8'         & 130        & 134        & 152        & 168         & 200       & 
240        & 340        & 520        & 340        & 520         & -             \\
8'         & 130        & 134        & 152        & 168         & 200       &
240        & 340        & 520        & 340        & 520         & -             \\
8'         & 130        & 134        & 152        & 168         & 200       &
240        & 340        & 520        & 340        & 520         & -             \\
    \hline
\end{tabularx}
    \end{table}
\end{document}

Answer 2

Replace

\color{white}\fontsize{6pt}{6pt}\selectfont \centering Text  &

with

\color{white}\fontsize{6pt}{6pt}\selectfont \centering\arraybackslash Text  &