There's a notion called "reality checking" used amongst therapists. Find about out and learn how to do it often till you get it.
An example is just what you have been marniadec, but if you think about it as a tool and find other ways to use it, eventually it will sink in. Learning to doubt your own assessment of this situation is probably a very good idea.
There are situations i have to do it but they are not about my appearance so much.