I sew my HST by using the grid method. I mark my grid squares about 1/2 to 1 inch larger than I want my finished squares. I sew on all the lines, then press the large piece to set the stitches. Then, I cut on all the cutting lines and iron the squares open, usually pressing toward the darker side of the triangle. Then, back to the cutting board and I cut the squares to size. This way, there is no bias stretch as you sew. My squares all come out the right size and I have no problems sewing into larger blocks. Yesterday, I sewed and cut 72 HST this way.