As a quilting teacher, I can tell you that there are no no new mistakes; just new threads on old ones. I am sure that I have made every mistake out there, and just to be sure, have repeated a couple on occasions. When the problem is taking over, just step away from it for a while. I have one UFO that had been sitting in a box for years. When I finally took it out, I decided to finish it, mistakes and all! Well, OK, I did fix one mistake...I had to...that row was INCHES longer than the rest!
And when all else fails, you can always slice and dice it for a border or binding on something else. Bottom line, it's probably not as bad as you think.