That is a very attractive quilt - T-shirt quilts sometimes look kinda muddled, but yours is nice and crisp looking!
I agree with the others about borders and thread colors. With so much white on the top use a backing fabric on which you can use the same color bobbin thread as your top thread: even thought the thickness of the top will bury your quilting threads more than on a regular quilt, you still want to minimize pop-ups.
Alison