Oh, I tried a test block today. Yes, surely, you have to sew a scant 1/4" seam to achieve the 8 1/2" raw edge to raw edge block! If you girls decided to cut your 4 beginning squares of fabric a bit larger so as to be able to trim your block to the 8/ 1/2" -- just a tip about that: remember to put your center seam on the 4 1/4" line both side to side and top to bottom before you cut the outer edges! A full 8 1/2" block is great, but, if you happen to square up with two sides of your block on lines on your mat and then cut only the other 2 sides, it means that the center seam is bound to be in the wrong place...