Here is my method, which seems a bit simpler, and always worked well for me:
You will have 3 sections: Your PP'd NYB points, the inner arch which looks like a 1/4 circle, and the outer top arch which has a squared edge on two sides.
Fold your NYB point block in half, and place a pin at the halfway point on the top of block. Fold the top arch piece in half, placing a pin at the middle on the inside curve.
Using sharp scissors, made 1/8" deep cuts every 1/2" all along the INSIDE curve. With right sides together, match the center pins and pin together at the midpoint. Line up the straight side edges and pin. With the top arch on TOP, stitch 1/4" seam along the curve for about an inch. Stop and realgn the edges. It helps to use a stilleto or pin to ease the fabric into position. Go slowly.
Repeat process for the bottom arch piece, except you make the 1/8" clips on the INSIDE arc of the NYB pieced block.
Good Luck!