That is a beautiful quilt and whatever you decide to do with the borders, it will still all be gorgeous. Don't feel bad about the mistake though. I'm assuming you're a veteran quilter and feel like you should be above a mistake like that, but we all have our moments. And those dang mitered corners are a pain in the rear!!!
Check out this bad boy picture below. You wanna talk about waves. :) I didn't redo, just hoped it would "quilt out". Second picture is an after picture.
Best wishes for whatever you decide!