I don't know if this helps at all, but when my blocks are a little off, I cut the solid squares exactly to the right size, and then use them as a "guide" to square up the slightly wonky blocks. For example, if my solid square is exactly right, and the block is off by 1/8, I line it up so that the seam is 1/4 on the solid square and 1/8 on the block, and it comes out (close to) right once they are sewn together.
Cheers,
Jan