From what I have read here, there should be a small overlap of the seam or the label tends to pull apart along the seam. I roll the tube into a piece of the paper in question and mark about 1/32 - 1/16 extra past the overlap. I then cut it square to the other side and use this as a templet to size the label. Try a few test labels before casting to get the feel. be sure to have a slight overlap.
Charles