Have you fabric leftovers from the top?
May be you could make a 5,5 inch strip of blocks with those fabric.Then cut them lengthwise,p.e. a 5,5 inch strip .The backing could be: narrow strip backing, strip blocks (or coins etc) and the rest of the backing.
Of course you could cut the backing in 2 pieces of the same width or cut them any size you like.Iwasjust usingthenumbers to make it easier to explain.Hope I made a bit of sence LOL.