First, instead of cutting 12 inches off each side, why not just cut 24 inches off one side. The size will be the same and you can use a 24 inch piece of fabric much better than two 12 inch pieces. And, even though the seam will be offset, once you quilt, no one will even notice. Second, why not just rip? I rip all the time and it comes out fine. Just spray the edge with water and iron it. It lays down just fine.