When I make a half sq triangle I always cut a square 1 inch larger than what I want the finished block to be. Put two pcs together and draw a line diagonally across. Sew on either side and cut on the drawn line. Press open and viola, you have two half sq. triangles. Then square them up to the correct size. For instance, if you want a 2 in. finished sq. Cut a 3 inch block. After sewing and cutting in half, you would sq. it up to 2 1/2 inch because that would be with the seam allowance/ HOpe this helps. Marge