When I need to widen or lengthen a quilt I tend to use what scraps I have leftover. Here's a pic or two how I did some. I like to add colored squares between the neutral squares, diamonds along added sashing/borders or just add extra sashings and borders before the last border. On one scrappy quilt you can see I just stitched a bunch of the scraps and then cut them to go along the top and bottom to lengthen the quilt. Anything to uses up the scraps. Sometimes I'll even add them to the backing if I have to piece it anyway.