Leigh, here's what I know: You need 1600 inches of jelly roll strips. My understanding is that the cutting off of 18" ensures that your seams are staggered. If it were me, I'd sew all the strips together to get the needed 1600 inches, then fold it in half and see where the seams lie. If they look staggered, go for it. If not, cut a chunk off one end. Can't wait to see your quilt!