Sounds like you need to try a courage spell. I suggest using several of the many courage spells here across a long period of time, and it can't hurt to come up with a short chant to use before you step into a social situation, such as a busy classroom or a party. Fire is an element associated with courage, so light red candles and face south (fire's cardinal direction) while performing your spells to bring those energies forth.
I always recommend changing previously written spells (such as the courage spells on this site or in your spellbook) to match your needs. If what you're saying doesn't sound or feel right to you, tinker with the wording until you feel comfortable with it. Your spiritual energies won't be as powerful when they're on edge and uncertain.
You might also want to try a few confidence spells. Yellow is a good color for this, especially concerning social situations for young people. I carry a sea shell that I blessed with a yellow candle with me for confidence on a day where my nerves might get the best of me.
And if you're still not comfortable coming out of your shell (no pun intended), you can include in your spell a little bag or pouch with pine needles, nutmeg, dried flower petals, a pinch of sugar, and, if you can manage it, mandrake root shavings. You can carry this around with you with the shell after you've charged it with energy with a simple ritual.
Hope that helps! Any questions, let me know. :)