I'm new to knitting, I am knitting my first sweater and my pattern says to cast off for neck the 10 centre sts. At neck edge cast off on every alt row 2 sts twice and 1 st once. I have 46 stiches, does this mean, I should knit 18, then use a new ball of yarn to bind off 10? Then I should knit the last 18 with the new ball? Any help would be appreciated.