I used the Marti Michell giant dahlia templates. They have reference mark holes on the curved edges that you line up when joining pieces and it came out just perfectly.
I like that the 16 center points are not sewn together with a giant knot of seams and I'll use the same technique if I ever do a center like that on something else. The last 1/4" of all the center seams are unsewn and when you press them they just swirl around the center.