You can try blocking it: Dampen it then pin it down, squaring it up as you go. If you have carpeting, that's a good place to do it. USE STAINLESS STEEL PINS! You don't want to have rust spots. When it's dry, it should remain square. The only caveat is if you wash it again, it will go back to it's original shape, so you will need to quilt this one heavily.