Fitted Crib Sheet is a Bust!

Okay, the fitted crib sheet is still in the draft (or maybe I should say re-draft) stage.  Tried to fit it on the crib mattress at my daughter's place once it was done, but it is about 4 inches too long! I have no idea how that happened.
I put a pin in the spot on the sheet to mark where the end of the mattress is. Now I have to take the elastic off the end, (Oh, what the heck! maybe I'll just cut the end off and save some time!) Then I need to open the 2 side seams (which I had so carefully double sewed,) and cut 2 new side pieces out ( 7 inch squares), and re-sew the whole thing....  The sides of the sheet are a little loose, too, so I'll have to add more elastic... I really don't think I will be making too many more crib sheets from scratch.
Oh, well, live and learn, I guess!