I got a great tip on piecing backing from QB member Bellaaboo?. You put 2 length of your fabric, right sides together, pin and sew about 1 inch down both sides where the selvages are. Trim off the selvages. Open up the tube so that the 2 seams are in the center and pin them. Cut down the center of 1 of the sections. Take out the pins and open up the fabric. You will now have the WOF in the center with 2 even strips of fabric on each side.