Wow -this is amazing. Looks like you only have it on your planning board and no squares are put together. It will take on more life as you get it more together - have patience with yourself - you will love it, as will your son.
Depending on total size you're making I agree 1-2 thin borders and then a wider one. Or as one person suggested the piano key boarder which would be awesome but lots more work.
The number of musical fabrics is phenominal - you must have collected them for some time.