[TwentyThirteen] sidebar layout problem

Hello,

I am currently working on a Webshop with WordPress & Woocommerce, i used the original TwentyThirtheen template and modified it (child theme) for the owner’s wishes.

Now almost everything works fine, except for the Sidebar Widgets, the footer ends on some place, but the sidebar widgets will overlap the footer.

I aldready tested it on the original theme without modifications, it has the same problem!

How can i fixx that? Tried a few things but nothing really works..

You can see what i mean here:

https://img.mypolo.nl/johan/problem.jpg