TwentyThirteen footer full width

Hello everybody,
I am new to wordpress and I can’t figure out how to make my footer full width. I have set up a child theme and I want to start to fill the site with content, but I can’t get the footer to be displayed in full width.

I mean the #303030 Area on the bootom on Falzmaschinen-test.de

It would be great if someone could help me, because I am stuck for days.
Thank you