Making half square triangles larger is the way to go. I know all the books say cut 2 squares 3 and 3/8 inches draw diagonal line, then sew a scant quarter inch on both sides of line, cut apart. But this has never never been accurate for me. I would cut mine 4 inches then trim to 2 and 1/2 inches. Trimming is a pain if you are making lots, but it sure is accurate. Good luck, Looks like a graet block.
Donna