How can I broaden a caption?

I’m trying to extend a caption beyond \textwidth. I tried it with \makebox, however, that resuls in an error:

\documentclass{article}
\usepackage[left=2.5cm,right=2.5cm,top=2.5cm,bottom=2cm]{geometry}
\usepackage[demo]{graphicx}
\usepackage[english]{babel}
\usepackage{tikz}
\usepackage[utf8]{inputenc}
\usepackage{blindtext}
\usepackage{titlesec}
\begin{document}


\begin{figure}
\centering
\renewcommand{\arraystretch}{3}
\begin{tabular*}{\textwidth}{@{}ccc@{}}
  \includegraphics[width=0.31\linewidth,height=2cm]{dummy} &
        \includegraphics[width=0.31\linewidth,height=2cm]{dummy}&
        \includegraphics[width=0.31\linewidth,height=2cm]{dummy}\\
    \includegraphics[width=0.31\linewidth,height=2cm]{dummy} &
        \includegraphics[width=0.31\linewidth,height=2cm]{dummy}&
        \includegraphics[width=0.31\linewidth,height=2cm]{dummy}
\end{tabular*}
\makebox[1.2\textwidth][c]{
\caption{\emph{Title.} \blindtext}
}
\label{fig:mipLevels}
\end{figure}

\blindtext

\end{document}

Error message:

Missing \endgroup inserted.