It's easy. Sew three triangles together, base up, tip up and base up, like a W. Press both seams in the same direction. Do it again with the other three triangles and press the seams in the same direction as the first time. When you sew the two halves together, the seams will all circle around in one direction and the center will lie flat. I never have never left the center "open" as many people swear you should do, and my centers are always flat and secure.