Yes, the backing fabric needs to be square and even in order to pin it to the leaders to avoid puckers in the backing when the quilt is quilted. I do not like to rip my backing fabric to square it up, I prefer to cut it. Picture your backing fabric as a sheet of lined notebook paper. Fold the paper (backing fabric) in half with the lines running horizontal, place a safety pin on the fold at the top of the paper (backing fabric), open the folded fabric up (lines are still running horizontal) and now bring the bottom edge of the fabric up to the top edge. Spacing your hands about a yard apart and holding both the top and bottom edges even with one another, with your index fingers between the layers, "walk" the fabric between your hands back and forth until the two layers fall straight down without any "ruffles". When you no longer have any ruffles, unpin the safety pin and pin through both layers of fabric. The safety pin should go through the same hole at the top fold and a new hole in the fabric folded up to meet the top edge. The folded fabric can now be laid on the floor or large table and smoothed out to the sides, place a cutting mat under the fabric edges that need to be squared; place a ruler along the edge with a line on the fold and square up the edges as you would square a fat quarter getting it ready to use. You may need to move your cutting mat up depending on how large your backing fabric is. Move to the other side of the backing, cutting mat under the fabric, ruler on the fold and square up that side. Before moving the fabric off the floor or table place a safety pin on each side you just trimmed at the fold. Remove the safety pin at the top of the fabric. You are now ready to load onto your longarm frame; centering the safety pins over the center of the leaders on the frame, start pinning the backing onto the frame at the centers, working your way out to the edges. You should now have a squared and centered backing that will roll smoothly back and forth on your frame and ready to load the batting and quilt top. Good luck, take your time, and your backing will look as great as your front!