Hi, I have been searching for tutorials on the pinwheel and found what I think will help you a lot. This is the web address. www.connectingthreads.com/tutorials/Pinwheels-Intro_to_HSTs__D4.html. Hope it helps. When you sew the two sides together to complete the block, use the nesting technique, where you have the seam on the top squares, pointing up and the seam on the bottom squares pointing down and as you sew, it will push the top seam right into the bottom seam and thus your center seams will match exactly.