I seen something on a website regarding doing that. It said the if your block is not perfect (ie too small of a seam allowance), iron it to a piece of freezer paper that is the size the block should be. Then sew it to the other blocks, using the cut edge of your freezer paper as your guide. Then if you don't have the full 1/4 seam allowance, your block will still come out the correct size. Then just tear the paper off like you do when paper piecing. If you have too big of a block, just trim.