I can understand the confusion. If you don't have an easy way to fold them up, fitted sheets are the worst.
However, if you need some advice: Fold it in quarters (half in each direction), and line the seams in the corners up together. Then you can line up the two folds however you like, then fold the rest of it up to whatever dimensions you want.
Not that I've been doing this lately, of course... =^.~=
I can understand the confusion. If you don't have an easy way to fold them up, fitted sheets are the