So I had an afterthought... after making a little camper quilt this summer, that it was not big enough for the bed.
Always Think Things Through, or Plan Ahead, or How to Enlarge a Quilt
Original quilt size about 61" square, desired quilt size 90" square (king size).
Make 4 borders each finished size 15 x 90, so unfinished size 18 x 96 (to allow for shrinkage). Sew label into one of the borders, in the middle instead of corner as the corners will have a lot going on already.
Sandwich the borders with batting and backing, do quilting, finish edge with binding except for the ends, seal all edges to protect from raveling during wash. Wash all 4 borders (because original small quilt has already been washed and shrank).
Four borders joined, lay out on floor, lay out original small quilt on top. Measure to make sure it is centered. Top stitch opened up binding onto borders.
Turn over, cut batting to meet the binding seam from original quilt. Fold over edge of lining to cover batting, sew in place.
Whew! So what did I learn? Always Think Things Through, Plan Ahead. It can be done. It was a challenge and I did it. No, I don't recommend making quilts this way :)