Hi, it sounds that you have what it takes to take care of yourself! You know whats wrong and want to improve your way of life, and i look up to you for that!
Youve already made the biggest step, to make an appointment for therepy, now give it time and be confident that you can pull trough! By time it will get easyer to go, but dont be afraid, be proud because you are stepping up and defending what is most precious to you, yourself!
Dont worry about school firstly i doubt they will throw you out for cutting yourself, (its not seen the same as being gay...i am not justifijing what they did) and secondly you should worry about yourself before you think about anybody else!
Good luck and be proud of what you are achieving.