I'd advise you to it. I'll explain.
One of the hardest things for beginners in any art style, in my opinion, is the ability to share it with others. It's because, despite what viewers may think, it's a personal craft. This applies to artwork, stories, music, etc. I had to take an art course for uni, which was rough because I'd only ever drawn privately, and more-or-less feared showing it off.
As it turns out, if you want to improve it's a fairly important step. Disregarding feedback, it's a way to get comfortable with your craft and help boost your confidence for later works. It is very daunting just diving in, but the more you do it the easier it gets. But, of cause, be smart about where you post it...there are trolls everywhere, and you really wouldn't want to start off with bad experiences. I suggest DeviantArt since it's more in the artists control than the posters.
I will say though that I have similar problems. Whether writing (my preference) or drawing, I'm very reluctant to post things. I wish I wasn't, and it did get easier during the stretch where I was over it, but going quite a while without makes it hard to jump back in again.
I'll just end with this: most artists/writers are, to a degree, blind in regards to their own work. If you want to learn to get better, the best way is to display it and let the readers be your eyes.
EDIT: Although I'd say it's best to keep it away from the eyes of people from school that could get to you. Easy enough to do, just post without stating your real name, and don't give away the username to people you don't want to be able to follow it. I'd imagine those people don't have the skills or effort needed to stalk someone online.