Help! I’m currently knitting Little Jocket Wrap Sweater from a Sublime pattern book. The sweater has a shawl collar that is knit seperately. I had no problem seaming the collar around both sides and back of neck. But now the pattern states to place the left side over the right and seam to cast off stitches along base of front neck. This gives you three layers to seam together. What’s the best way to do this? Lost and confused!