This is a quilt I made a few years ago for some friends that were getting married. They now added height to their bed and wanted the sides longer.
So this is what I did for them
I cut two long strips of fabric that I quilted.
This is a pic of the backside before I washed the blue marker out.
I bound the bottom edge and added to the sides as it was a little short and laid them under the binding of the original quilt and sewed on the binding line.
I'd say it came out pretty well. The whites are slightly different colors, but it still works.