I think pressing damp material causes it to stretch, which seems to be what happened to your blocks. I firmly belong to the "make it big and cut it down" club. I once used precut squares and after I got the HSTs made I starched, pressed and trimmed them. You will lose quite a lot of finished size in your king size quilt, but maybe you could just make more, or add on a boarder. At least they would not be totally wasted.