This is not advice for you, just a story.

I had a bag with a dark mark. I covered it over with a pretty leather flower. Or several. To make it look intentional. I've also seen (these are not recommendations, just stories and thoughts), a person took their bag's boo-boo and made it more so. One bag had this giant circle on it...wish I could find the picture to share. Your mark looks like a HEART to me. You could make it look more like a heart, fill the outline. So, you'd have a brown bag with a black heart on the back. It's kind of like not ignoring the elephant in the room, it's more like pointing him out and riding him. Or, leather paint applied to the spot to make it less noticeable, or some matching color shoe cream. Or, leave it be!

Options!!