I have some backing fabric for a quilt I am doing for my husband, but it is like 5 1/2 yards long. I have cut the piece in half (width) and I need to piece the back together, so I need to cut about 12 inches off each l-o-n-g side (length). But I only have a 24" cutting mat and ruler, so logistically how to I cut a straight line down the long edge? <Is this as clear as mud?> I'm sure some of you veteran quilters can offer some advice for me. Thanks so much!