Here is another thought, Your name attached to this quilt. What if the buyer points out your mistake to everyone she shows it to? Will it affect your business?
I would have to correct this mistake just for my own piece of mind.
I'm so sorry that this happened to you, I do take photos of my quilts at different stages, while they are up on the wall, put them on my puter and give them a good look over, even rotate the photo. I have caught many mistakes early on by doing this. Good luck on your quilt.