4 blue boxes

Hi! I changed the page for the first box and it lost the icon. So I took the icon file from the theme and uploaded it as featured image for that site. Now it looks streched and fugly. What’s the problem?

It’s like this: http://www51.zippyshare.com/v/XcN0ZxXW/file.html

Thanks in advance!