The truth is that you need to measure your block as it is assembled to be sure that each piece is the right size. If any piece doesn't measure correctly, stop right there and figure out what the problem is. Don't keep on sewing, hoping that things will get better as you go, because chances are they won't. Trying to square up after all the patches are in the block will not work, unless the block is very simple. Checking as you go is not as bad as it sounds, because once you get the hang of sewing a scant quarter inch seam you will find that you need to measure and square up less and less often.