I started by sewing the other back neckband peice to the one sewn on the shirt, leaving enough of an opening to turn it.
I turned it right side out.
I will hand stitch the opening later.
I gathered the front, and sewed on the front neckband.
I’ll admit that I pinned the neckband together and tried it on. It will be wearable but if I make it again I will be making a few changes.