I TOTALLY FEEL YOU!!!! I feel the exaxt same way SOOO much of the time.... fortunatley my family isn't that obvious about it, but I live in an area where EVERYBODY is an overachiever, and both of my parents are SO incredibly successful... I'm not exactly at the top of my game right now (anxiety, depression, ADD, other suff yet to be diagnosed), and I'm not anywhere NEAR as beautiful as the girls I'm always surrounded with who spend two hours in front of a mirror each morning. I'm a perfectionist because of it, and honestly, that just adds to my depression and SERIOUSLY impacts my self-esteem issues.
Point being: YOU DON'T HAVE TO BE PERFECT!!! EVER!!! Trying to be perfect all the time is like doing this

over and over again. I know, however, that attempting to accept yourself, esepcially when your family isn't as accepting, is one of the hardest things to do in life. My advice? TRY, just really really TRY, to take little steps towards bulding up your self-esteem and confidence, and let your mistakes go. Celebrate what you do correctly, even if others find it trivial, and if you make a mistake, don't look at it emotionall, look at it critically and say, "You know what? I can let this pass."
And above all, never, NEVER, EVER try to please everybody!!! That is just emotionally and physically exhausting, especially when you should be focusing on YOU and how YOU can be the best person you can. Try to talk to your family about how they've hurt you and are hurting you, and I will hope and pray they listen.
Good luck, and TONS of love from a fellow "black sheep"!!!
~muse