Can you post a picture of what you have completed? Without a picture, I'm thinking I'd bands do of the quilt fabrics equal to 7" on each side of the quilt, then a one color or print 7" border all the way around. I would not use a plain fabric for the first add on (the two sides one). It will look like just - an add on. A pattern like stripes or something with HSTs or 4 patches will make it look more planned.