I've followed
Chapterstyle Memoir: Picture on page left, chapter opening on page right
to get a picture opposite the part page in a two-sided document prepared with memoir. My document has outer margins that are larger than the inner margins. To use the full width and to get a centered picture opposite the part page, I use the changepage package's adjustwidth command. However, the picture is not centered although some dummy text I used for testing purposes is. The following MWE illustrates the problem:
\documentclass[a4paper]{memoir}
\setstocksize{29.7cm}{21.0cm} % A4 stock
\settrimmedsize{27.94cm}{21.0cm}{*} % 27.94cm = 11in
\setlength{\trimtop}{0.0cm}
\setlength{\trimedge}{\stockwidth}
\addtolength{\trimedge}{-\paperwidth}
\settypeblocksize{23.94cm}{12.3cm}{*}
\setlrmargins{1.13cm}{*}{*}
\setulmargins{2.0cm}{*}{*}
\setmarginnotes{\onelineskip}{6.15cm}{\onelineskip}
\sidecapmargin{outer}
\setsidecaps{\onelineskip}{6.15cm}
\usepackage{tikz}
\usepackage{lipsum}
\usepackage{changepage}
\checkandfixthelayout
\usepackage[pdftex]{hyperref}
\begin{document}
\part{First part}
\cleartoverso
\begin{adjustwidth}{-6.15cm}{} % temporarily use full page width
\lipsum[1] % dummy text for testing, uses full page width
\begin{figure}
\centering
\begin{tikzpicture}
\draw (0,0) rectangle (12,12);
\end{tikzpicture}
\end{figure}
\end{adjustwidth} % switch back
\part{Second part}
\lipsum[1-6]
\end{document}
What am I doing wrong or overlooking?

figureandadjustwidth(and fix the typo in\end{adjust width}). Also:memoiralready has theadjustwidthenvironment, so no need to loadchangepage. – jon Nov 22 '15 at 21:43