To avoid this problem, I start in the middle of an edge (say, the middle of the top edge) and sew all the way to the other edge. The second line of sewing is from the middle of a side edge all the way across to the other side edge. When using a walking foot and quilting straight lines, I don't think I would ever start every line smack dab in the middle of the quilt. Hiding all those thread ends would drive me crazy!