[knitqueen]

The last stitch of ball 1, and the first stitch of ball 2 are only attached to another stitch on one side so there will be a bit of a gap there. You can use the tail yarn of the second ball to try to tighten up that gap, but I imagine you'll be doing some kind of neckline finishing, maybe picking up stitches around or whatever, and that will likely solve the problem in the end.