The CO is usually a few inches shorter than the knitted item will be around. To join, you just knit the first CO st and snug up the yarn so there's not a gap. Since your co is short, you can pinch the cord and pull it out between 2 sts and push the sts towards the end and join that way. You may need to keep doing this for a couple rows until it gets longer and the sts will fit around the needle well. Unless you have too few sts, then they may not fit around at all.