I would get a different fabric (probably dark blue) and add wide borders all around. Could do some fancy quilting in the wide borders, and I think it would frame everything else. An alternative to a solid dark border would be a printed fabric that has a mixture of colors that coordinate with the colors already in the quilt.
It won't get wonky if you pre-cut your borders to size. Measure through the middle and use that measurement to cut your border. Before sewing, match middle of border to middle of quilt, match quarters, etc. When you sew, if you have a little excess border between pins, ease it in. If you have a little excess quilt between pins, ease that in.