Hi toomuch00! i also went through a similair situation in high school and it really is very painful and torturous to go through! some things that helped me include repeatedly telling myself that everyone makes mistakes and just because i made a mistake doesnt make me any different! everyone forgets the answer to a question in class and everyone makes a slip of the tongue. no one is perfect.
there was one person in particular that id get intimidated from so id try and break down the barriers by making sure to notice when she didnt do something perfect. not to put her down, of course, but to show that no ones perfect. even if i did say the wrong thing, chances the next second people wont even remember what you said.
another thing was pushing myself to go past my comfort zone. meaning, dont just hang around with the girls you always spend time with, give a “hi how are you” to someone you usually dont. dont avoid get togethers because you dont feel comfortable, do the opposite- go and try to participate in some way. start with something tiny and work your way up.
recently i heard a shiur from rabbi brezak about chinuch, but i think it can apply here too. in seaworld, theres a whale named shamu that can jump 22 ft into the air. how did the train a whale to do such a feat? they set him up so that the whale cant fail. the whale had to jump over the rope? so they started by putting the rope underneath the whale and rewarded him when he went over. slowly slowly they raised the rope and the whale jumped up higher with it. set yourself up to succeed! dont aim to be the head of G.O.! just give a hello to someone new. and work ur way up.
lastly, write a list abt all the positive things u can think abt urself. and refer to it. remember U R NO DIFFERENT THAN ANYONE ELSE! even if u feel different, its just you feeling it, but its not true! you are just as special as everyone else with your own special attributes and talents.
keep repeating these things to urself and keep a record of when u do succeed and give urself a pat on the back!
sorry abt the longwinded post, but i had a lot to say. hatzlacha and keep us posted!