Are you going to be sewing these diamonds into the stars? If so you must leave 1/4" at end for turn under.
If you can make a Mylar template of the point of the star to the sewed seam - but make sure it's the finished size of that star point, put on wrong side of fabric and press down the 1/4" seam.....some will remove the Mylar and brush a bit of starch on that turn under....but doing this on all points of each star will make it easy to then sew them onto the block, either by hand or machine.....just one way of doing it...