It is easier to HSTs without cutting the squares into triangles -- cut the squares larger, draw center line on back of one square, sew 1/4" down both sides of line, cut triangles apart on centerline, then draw center line on back of one HST, place 2 HSTs right sides together, sew 1/4" down both sides of line, cut apart on centerline. Then square up the QSTs using your favorite method. That way, you don't have to handle the fabric on the bias and there is less chance of the blocks stretching.