When I get to the center of a 6 or 8 pointed star, I take the last quarter inch (that I have not stitched down) and twist them all in a circle fashion, sort of like those twirly things on a stick that kids spin by blowing on. Then I use a small hammer or the rounded top of a screwdriver handle and really press hard to flatten the twist. It kind of looks like I'm trying to kill my quilt, but it really works well fo me