extend the "checkerboard" far enough into the border to complete your diamonds along the top, bottom and sides; then add one or two borders and you'll have a queen size big enough to be useful to two people. brown border. either an orange back or a brown backing-as-binding. pale yellow would be inconsistent.
and for cryin' out loud ... quit obsessing over a few gafarbles nobody but somebody not good enough to judge will even notice. take your mother to dinner during the time you'll save. donate the savings in headache remedies to a local charity. if you're gonna pick up a needle and thread for anything but the binding ... use it to do the quilting.
you have nothing to prove. do you? besides ... a quilt should enhance your life ... not swallow it whole.