I agree with laurlync. But there is a lot of bulk in that center and that might be where you are having problem. If you can't get the fabric to lay flat, it will be distorted. Eleanor Burns had a method for getting those centers to lay flat. No expert on the internet but I would go to her web page and search for pinwheels. She undoes a few stitches and the center does lay much flatter. Pinwheels are NOT my favorite block either !!
