When I do a piano key, I have the borders 'chase' each other. Sort of log cabin style. Here's some instructions and a very rough sketch
1) add the border to right side. Make it even with the top, have extra piano keys, the width of your border. Leave an inch or two unsewn to the quilt at the bottom.
2) Add the top border, start even with the left side and end it even with the edge of the border on the right
3) add left border
4) add the bottom
5) now sew the little bit of the first border to the lower right edge of the quilt and the edge of the bottom border.
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Here's an example of a quilt with this piano key method (it's the second quilt, the star)
http://www.quiltingboard.com/picture...s-t261037.html