I am not sure I can explain how to avoid the curves when cutting fabric, but here goes. I cut from selvedge to selvedge with only one fold in my fabric, in other words approx. 21 - 22 inches long. I put my long ruler on the fabric, take a second ruler, usually 6"sq. ruler and line it up with the fold on the fabric. Then I butt the other ruler up against it, remove the 6" ruler and cut the width of the strip I need. On the very first cut you need to cut a strip a little wider and turn it around so the other side will be straight too. If I am cutting multiple strips, after about 5-6 cuts I again put the 6" sq down to restraighten the fabric. does this make sense to anyone. Marge