Header margin bigger

I'm trying to make the header "margin" bigger. It is to close to the edge. I've been trying to make \setlength{\headheight}{10pt} larger but then the page number moves to much down?

Any thoughts?

\documentclass[a4paper,12pt]{report}

\usepackage[margin=2cm]{geometry}
\usepackage{fancyhdr}
    \pagestyle{fancy}

\lhead{\nouppercase{\leftmark}}      % Set chapter in left header.
\rhead{\nouppercase{My University}}  % Set my university name in right header.
\setlength{\headheight}{10pt}        % ??????????????????

\begin{document}
    \chapter{First Chapter}                               %
    First chapter's content.
    \clearpage
    \section{Hello}
    The header is to close to the edge..
\end{document}