Thanks to all! I believe maybe the problem arose with the pressing even tho the strips appear to be well-pressed and of the same size. I did starch my fabric before i cut the strips and used a press to do it. but i did not press again until all 5 strips were sewn together. All the bands match precisely when sewn. it is just the center square that is consistently OFF by quite a bit. I inspect these strips and blocks before cutting the diagonals and they LOOK fine. I'm not hearing this is a common problem to others who have done this quilt so hopefully next one will go better. i do LOVE this pattern!