I could be wrong, and if so forgive me. I think a little of the problem might be in the squaring up. It kind of looks like the upper right square is not squared where the center seam between your triangles goes from corner to corner. They should have given better directions on squaring up. I would use a square ruler and be sure the 45' line is on that center seam. If it is off by even a little it will mess up the matching of seams. I would also press the way Nativetexan suggested.