When I do any HST blocks, I always round them up to the next whole number, say the pattern says cut squares 2 7/8", I cut 3" squares. Then mark the diagonal mark point to point, sew a scant 1/4" on either side of the drawn line. Cut on the drawn line, press your seam, either open or to the dark side, being careful not to stretch, then trim to the correct size, which in this case, would be a 2 1/2" square. I found out a long time ago that a scant quarter inch seam works better because it allows for the fold which takes up a little bit of the final size of what ever you are making. It's easier to make the squares a little oversize and then trim than to be sad because it doesn't fit in your final block. Hope this helps, and hang in there. :thumbup: