You do not need to be concerned if you have basted the quilt with glue or pins because it is stable. It is true that the LWG is less stretchy than the CWG. (width of grain). Most longarm quilters prefer a crosswise seam to join sections rather than lengthwise because of the way a lengthwise seam distorts the rolling of the quilt. I do think it is important to put the backing on straight with the face of the quilt to minimize stretch on the off-grain.