Hmmm, mine were all cut the right size. I'm sorry that you are having the problem. You can just make the quilt a little smaller, I think. Or if the cost of new fabrics is not going to be a burden that would probably be fine too.
Of course, here I am dispensing advice and I have only made one quilt for kids and have not even finished it yet. There might be other's who really know the best answer!