When I do straight line stitching I usually do a diamond cross hatch, spray baste the sandwich together and use blue painters tape (1.88" width). I start on the longest diagonal and tape, pinning in the center of the tape to hold as you feed it through the machine. Then I use a spacer tape positioned next to the first. Once that is in place, remove the first tape and position next to the spacer and pin. Remove the spacer and save for the next run. Now you can sew down both sides of the tape again. I sew in one direction on the right side, and the opposite on the left, so that the bulk of the quilt is always on the outside of the needle. Once you get those diagonals done, you still have to mark and sew the opposite direction to create your cross hatch. I just finished one without batting, using Minkie for the backing and I didn't have any distortion by doing it this way. I have done as large as an 80" sq. quilt on a 6 1/2" throat machine using this method.