I am having trouble getting my half square triangles to be sewn to a regular square; they don't match exactly so the points are off. I know that you cut the half squares 3/8" bigger. So I am making 2.5 regular square and the triangle square I cut 2 7/8. But when I go to match them up to sew, they don't match--the half-square triangle which is now a square is bigger??? What is the problem? Does anyone else have that problem? What must I do?