I love the stripe fabric with it. It adds a little color which kids love. I think if you add the stripe it will look great no matter if you border it like you show in the pic or use it as binding. No need to add anything else. He will just be happy to have a quilt from you, and as an added plus it's adorable! I do really like the idea of cutting that stripe on the diagonal if you feel like going to that much trouble. Whatever you decide will be great, but yes use the stripe.