I have an easy solution that i use for corners. It isn’t as stunning as miter but makes it quick for those fast projects. On the short sides I do piano keys along top and bottom. On the longer sides on the left and right, i sew a rectangle shape that is a bit past the corner of the quilt top on both the top and bottom of the strip. I will pick a color that will be nice. If I plan, I can use this same fabric on the last piano keys across the top and bottom. For example, if the piano keys are bright and I use black rectangles at the corners with black piano keys on the ends of the top and bottom, it causes the piano keys to float and I dont have any fussy points to match or make work. Again this solution isn’t for everyone.

Darcyshannon do you have a photo of what you've done? If so, please share. It sounds interesting!

Glad to read that I am not the only one that has problems with this type of border. I never would have thought about adjusting the seam either. Thank you so much especially as my current project will have piano key borders with a corner block the timing couldn't have been better

I have also mitered my piano key borders at times. However, if you are running short on your border, take a scant 1/4" stitch on a few of the keys to get it to the right length. Likewise, if the run is too long, take a wider seam to make it come out. Piano keys are so forgiving. Nobody will ever be able to tell.