It's a beautiful quilt ... and IMHO you want to focus on the quilt, not the border. A piano key would be too heavy looking against the delicate-ness of the blocks.
Here's what I'd do ... extend your Irish chain blocks into the border to complete the diamond of the chain. Then the rest of the border would be just the plain white background .... take a look at this quilt and you'll see what I mean but am not explaining well ...........
http://www.quiltingboard.com/picture...h-t213094.html
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