As long as your stitches fit on the circ, you can use that for as long as you can and then switch. One way to avoid a gap is to overlap the first and last stitch of your cast on, basically take the last and first stitches off their respective points and switch them. I generally just use the tail from my cast on to close any noticeable gap--simpler.
"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