This is just a guess but when you cut your squares up, the outside corner stays the same size. So I think that your squares need to be cut at 8.5" I would just find a piece of paper and draw it out. When you cut down the center, your strip (the one that looks like sashing) should be 4.25"
OOPS, that is a 12" finished. That is going to be difficult because when cutting the center of the 9 patch, the size of the square needs to be divisable by 3. Hope that makes sense.
Last edited by ManiacQuilter2; 03-30-2016 at 04:33 AM.