You might try cross hatching. I do mine by laying a length of blue painters tape along one of middle diagonal lines and then stitching next to the tape. The tape is your guide to a straight line. Then just move the tape across the quilt and go down the other side. Keep moving the tape. When it stops sticking use a new piece of tape. You never have to turn the quilt except at the ends of each row. Make sure you alternate which direction you hit each time to prevent puckers.