I agree that it looks finished as is. However, I am a border person and it almost looks like you've auditioned fabric beneath. What about piecing a border with fabric from the mice cut to just bigger than block size so there are no cornerstones? Or, as suggested, black, or even the directional print with the "down" side towards the quilt on all sides. If you have plenty of that, it could be a wider border and become a real part of the Disney theme.