New to quilting, but just thought (if it's even possible). What about running a basting stitch along each border piece to create a very slight ruffle effect. It would then look like the waves belonged and would take up the excess fabric. Then the border wouldn't even need quilting since it would need to look a little puffy. Then bind as usual. Your quilt is beautiful. I love your colors, pinwheels, and prairie points. Is this an original design or a pattern? Good luck!