When I did mine, on the strips of opposing blocks, on one block press toward the star point and the other block press away from the star point. When you join the 2 blocks together you can nest the points. Then the long center seam I pressed open.
Also, because there is a fair amount of bias on these, when I have a wavy piece I spray with starch and hold a hot iron over it - not pressing, just heating. The bias wavy part will shrink back to shape.