Whoops! I saw “3 instead of 4” and I immediately thought of footer-widgets when I replied, sorry about that (its been a long day full of multi-tasking).
To get the images to all be the same size, download and run a plugin called Regenerate Thumbnails – http://wordpress.org/extend/plugins/regenerate-thumbnails/ and it should regenerate all of the images at the size you have selected in the widget.
