I like the quilt without the sashing, but it's also pretty with it. I think I would use cream setting triangles, and cut them bigger so that when you trim the edges go from corner to corner. But trim at one half inch, not one fourth inch. Then when you make 1/4 inch seam on the borders, your quilt will "float" Also that way you NEVER cut off points! ! !
I love piano keys. I have made too many of them. And your quilt really could use the little extra size.