How much do you have to add? If it is about 12 inches, I would cut 2-12 in. strips by width of the quilt. I would pin one piece to the back of the quilt,right side facing the quilt and raw edges matching up (cut a strip of batt and pin along it also) I would then pin the other 12 piece right side laying on the right side of quilt and raw edges matching. I would sew across all of the raw edges across the the quilt and addition. Then I would flip both of the strips and batting up and press with an iron. If everything was laying nicely I would quilt that section straight out to the edge (bead board style) and then proceed to the opposing edge in the same manner. When both sides of the quilt were finished, I would then do the top and bottom in the same manner. Good luck and it really shouldn't be too hard.