I would suggest doing this as well. If you need both length and width added to your backing, cut the backing in half the other way and add another strip of scrap that way as well. Looks more planned as well!

I agree and have done this method on several quilts when the width of the material I had for the backing was not wide enough. And I have made three sections for the backing and I put 10 inch piece in the middle of the quilt backing using either the same as the back and on one, another color with a design in it that coordinated with some of the colors on the front. And then the two side pieces were the same sizes. Hope this helps....

I would not recommend this. Having seams going two directions is more difficult on the longarm quilter to make it quilt evenly. Most quilts are loaded with the backing seam parallel to the bars. A seam in the other direction will not stretch as much as the unseamed edges, resulting in puckers on the back. Ideally, a backing should have no more than one seam. Really ideally, backings should be wide fabrics with no seams. You might look at Christian Lane Quilters for their 'fatbacks'. They often have sales and sometimes their clearance end of bolts are plenty.