I don't think that would work. You have to compare the finished sizes of the squares. It's going to depend on the pattern. a 2.5" square would finish at 2" if it's used as a square. the 3.5" squares would finish at 3" if used as a square. So 3" is 1.5x 2", and you may need squares finishing at 2.5 x 1.5" = 3.75" if you use 3.5" squares, so my mistake, 4" squares might work. I'll echo what someone else said - try a test block.