You can sew down the edges of the center flat, or if you like it to have the 'diamond' look, pick up that side of the center block and fold in (like a cathedral window block) and sew it down by hand. If you look at the "Gallery of Quilts" section of this site, you'll see there is a whole section of 10 minute block quilts. Look at the ones where folks have folded back each side of the center block and sewn it down....it gives the 'round' look to the blocks when you see the whole quilt shown. Have fun with it -- like every other method you make it your own by your fabric choices, etc...