I am creating a longtabu with a caption. As you can see in below example the text is indented to far to the left. I attached a minimal example. Could somebody please explain what I am doing wrong?
\documentclass[11pt,a4paper]{book}
\usepackage[a4paper,showframe]{geometry}
\RequirePackage{luatex85}
\usepackage[table]{xcolor} % xcolor: colors
\usepackage{tabu}
\usepackage{longtable}
%% Table captions above tables
\usepackage[
singlelinecheck=false
]{caption}
\begin{document}
\tabulinesep = ^2mm_2mm
\begin{longtabu} to \textwidth { X[1] X[1]} % {<input1>} cell/cell size;
\caption{123123} \label{123} \vspace{-1em} \\
\rowfont{\leavevmode\color{white}\bfseries} % Set font color for the first row
\rowcolor{blue} % Set row color for the first row
1 & 2 \\
\endfirsthead
\caption[]{123123 - continued} \vspace{-1em} \\
\rowfont{\leavevmode\color{white}\bfseries} % Set font color for the first row
\rowcolor{blue} % Set row color for the first row
1 & 2 \\
\endhead
\everyrow{\tabucline[.4mm blue]{}} % Set line between rows
3 & 4
\end{longtabu}
\vspace{0.5em} % Vertical space at table end
\end{document}