http://www.stolescreated.com/how-to-make-a-stole.html
Try this link. If the link does not work, I googled 'how to make a stole', and it's the first thing that came up. You have to scroll down a ways, but it does show how to make a curved neck. You'll have to adjust the size, since this is for a clergy stole, which I think is bigger than what you want. If this doesn't work, try searching on confirmation stoles - they might be a better size.
Good Luck