Before I call an image done, I do two last things.
First, I look for a critique by someone I can trust to give me an honest opinion. In this case, I ran it passed one of my friends, a talented animator whose eye for detail is invaluable. It was his critique that brought the horn tangent problem to my attention.
Lastly I will do a few test prints, no matter how my monitor is adjusted, it's no comparison to seeing the image printed out.