This is very simple...but if you don't have the time to sew it...you may check it out in Etsy...I saw it there...but it was sold out and so I made my ...
Step 2: Sewing The Edges
I wanted the edge to show behind the neck when I wrap the warmer...so i folded wrong side facing each other...with once side being longer than the other so that i could fold over and stitch. Sew keeping a 1/2" width from the edge and leaving 1" on either side un-sewn ( which makes it easier to tuck in later ....else you will have to unpick!)
Now tuck in the edges in both corners and sew a half and inch border on the remaining 3 sides.