You have to sew them up. The cast on stitches are not attached to both parts of the sweater, so when you're done, just stitch them closed. You can snug up any loose stitches then, as well, by pulling them from the back a bit.
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog
IngridKH on Ravelry