Set margins don't apply to titlepage

Question

I use scrreprt for my thesis. I set the margins using the geometry package. But those somehow don't aply to the titlepage. It shows much more space on the right side, which, I reckon, is due to the two page character of scrreprt. How do I get my titlepage to be centered? I am thankful for any ides on how to achieve my goal.

\documentclass[12pt,a4paper]{scrreprt}
\usepackage[left=2.5cm,right=2.5cm,top=2.5cm,bottom=2cm,includeheadfoot]{geometry} 
\setlength{\headheight}{15pt}

\begin{document}
%titlepage
\thispagestyle{empty}
    \begin{minipage}{0.75\linewidth}
        \begin{center}
            \centering
            %University logo
            %\includegraphics[width=\textwidth]{logo.pdf}
            \rule{0.4\linewidth}{0.15\linewidth}\par
            \vspace{2cm}
            %Thesis title
            {\uppercase{\Large This is a very long title going over three lines and it is still not completely done\par}}
            \vspace{2cm}
            %Author's name
            {\normalsize submitted by}\\{\Large Name \par}
            \vspace{2cm}
            %Degree
            {\normalsize xx xxxxxxx xxxxxxxxxx xx xxx xxxxxxxxxxxx xxx xxx xxxxxx xx}\\{\Large xxxxxxxx xx xxxxxxx \par}
            \vspace{2cm}
            \end{center}
            %Date
        \begin{flushleft}
            \vspace{1cm}
            \begin{tabular}{ll}
                {\Large xxxxxx, August 2017}&\\
                &\\
                {\Large Student Number:}&{\normalsize xxxxxxxxxxx} \\ 
                {\Large Supervisor:}&{\normalsize xxxxxxxxxxxxxxx.}\\
                {\Large Co-Supervisor:}&{\normalsize xxxxxxxxxxxxxxxxx}\\
            \end{tabular}
        \end{flushleft}
    \end{minipage}
    \clearpage
\end{document}