Header and footer on A3 papersize in a A4 papersize report

How do I get the line under chapter 1 to follow the whole A3 paper? like the line at the bottom does.

 \documentclass[a4paper,11pt,fleqn,twoside,openany]{memoir}
\usepackage{lipsum}
\usepackage[dvipsnames]{xcolor}
\makepagestyle{Uni}
\makepsmarks{Uni}{%
\createmark{chapter}{left}{shownumber}{}{. \ }
\createmark{section}{right}{shownumber}{}{. \ }
\createplainmark{toc}{both}{\contentsname}
\createplainmark{lof}{both}{\listfigurename}
\createplainmark{lot}{both}{\listtablename}
\createplainmark{bib}{both}{\bibname}
\createplainmark{index}{both}{\indexname}
\createplainmark{glossary}{both}{\glossaryname}
}
\makeevenfoot{Uni}{\thepage}{}{}
\makeoddfoot{Uni}{}{}{\thepage}
\makefootrule{Uni}{\textwidth}{0.5pt}{1mm}

\copypagestyle{Unichap}{Uni}
\aliaspagestyle{chapter}{Unichap}
\pagestyle{Uni}

\newsavebox{\ChpNumBox}
\definecolor{ChapBlue}{RGB}{120,200,240}
\makeatletter
\newcommand*{\thickhrulefill}{%
\leavevmode\leaders\hrule height 1\p@ \hfill \kern \z@}
\newcommand*\BuildChpNum[2]{%
\begin{tabular}[t]{@{}c@{}}
\makebox[0pt][c]{#1\strut} \\[.5ex]
\colorbox{ChapBlue}{%
\rule[-3,5em]{0pt}{0pt}%
\rule{1ex}{0pt}\color{black}#2\strut
\rule{1ex}{0pt}}%
\end{tabular}}
\makechapterstyle{BlueBox}{%
\renewcommand{\chapnamefont}{\large\scshape}
\renewcommand{\chapnumfont}{\Huge\bfseries}
\renewcommand{\chaptitlefont}{\raggedright\Huge\bfseries}
\setlength{\beforechapskip}{10pt}
\setlength{\midchapskip}{16pt}
\setlength{\afterchapskip}{10pt}
\renewcommand{\printchaptername}{}
\renewcommand{\printchapternum}{%
\sbox{\ChpNumBox}{%
\BuildChpNum{\chapnamefont\@chapapp}%
{\chapnumfont\thechapter}}}
\renewcommand{\printchapternonum}{%
\sbox{\ChpNumBox}{%
\BuildChpNum{\chapnamefont\vphantom{\@chapapp}}%
{\chapnumfont\hphantom{\thechapter}}}}
\renewcommand{\afterchapternum}{}
\renewcommand{\printchaptertitle}[1]{%
\usebox{\ChpNumBox}\hfill
\parbox[t]{\hsize-\wd\ChpNumBox-1em}{%
\vspace{\midchapskip}%
\thickhrulefill\par
\chaptitlefont ##1\par}}%
}
\chapterstyle{BlueBox}

\begin{document}

\thispagestyle{empty}
{\pdfpagewidth=2\pdfpagewidth
\textwidth=350mm

\chapter{example}

\begin{table}
\centering
\begin{tabular}{l|l}
1.1 & 295 \\
1.2 & 345 \\
\end{tabular}
\end{table}

\lipsum

\end{document}

• Please extend your code to a minimal working example (MWE), something others can copy and paste and compile to see your problem. Add a minimal preamble including \documentclass{foo} the code you have is not compilable, has a table environment which is empty and the \thispagestyle line is rather lacking a number of necessary }. As it stands it's not clear what your problem is, an MWE will significantly help others understand your issue. Oct 25, 2016 at 21:28
• I take it you are familiar with tex.stackexchange.com/questions/6834/…, so you know this isn't a standard operation. AFAICT, a3paper is not a page style. Even if you manually change all of the parameters normally set by geometry, that will not necessarily reformat the header. Oct 25, 2016 at 21:46
• Maybe you'll understand now? Oct 26, 2016 at 20:15

The easiest solution for your problem is to set the line using the fixed width 350mm, rather than use a leader that spans \textwidth:
\newcommand*{\thickhrulefill}{%