Category Organization Help

I am having trouble getting my categories to line up properly on the screen. I have them in alphabetical order, which is how I would like them to stay. When I click on the category it opens up and is supposed to be 4 acts (posts) in each row. When I get to the bottom is shows 3 blank spaces & 1 post then goes to another line to show the last post. Here is the link. http://entertainmentunlimited.com/category/impersonators/ If anyone can look at it and give me some advice I would appreciate it. 🙂