I like the idea of a border of the yellowish fabric that you used in the body of the quilt, the same width as you had in the yellow blocks that 'sash' between each block. Then I'd cut wider piano keys of all the fabrics you used in the center to make longer lengths, attach to the sides and then cut a scalloped edging to soften all the angular edges in the center. Then it doesn't take away from the beautiful blocks. Wonderful quilt!