We decided that the best way to do this would be to have 4 pannels on the back of the seat, using the cut off at the bottom as the back panels. We cut this 2foot piece of fabric in half and lined the first one with one side of the hardboard marking the center of the back of the sofa. We stappled this at the top just under the plastic tubing first. Then we stappled down one side, hemming a small part of the fabric and stappling in place. We then repeated this on the other half of the material.
Once these were done we attached the 2 side panels. We did this by first attaching fabric to the from of the arm and wrapping round untill it meets one of the back panels. this piece of fabric was also stappled just under the plastic tubing and hemmed to create a neat seam.