I haven't done pieced borders like that (only simple piano keys) but I read that if you need to adjust the length, you just adjust individual seams a tiny bit. For example, if your border is 1/2" too long you adjust 4 seams 1/8" or 8 seams 1/16" to do minor adjustments that aren't so noticeable. I don't know how it would work on a border with that much piecing but it looks like they all have some straight across seams that could be adjusted if needed.