Up to the stripes, it looks phenomenal. Do you have fabric to work with? In the one I did, the owner provided one or two fabrics.
I assume that you want to add a border that he could use - so I might add a border and semi forget the stripes. The final border needs to be bold and substantial. How about something like this
http://www.quilterscache.com/E/EntwinedBorder.html
It is straight, would frame it and might force the eye back into seeing a rectangle. It might look something like this(I threw it into paint), Good luck!!