Yes, practice makes perfect but it is nice to know what you are doing wrong. If you pop into a quilt store or JAF, you might want to take a look at an article in the current Quilty magazine Mar/Apr 2014. I make my HST a bit larger then press them with starch then do a final trim cut. If they are exact, your seams were find in the D4P so they should have been fine with the pinwheel. Good Luck !!