This kind of feeling is more common than you'd think, especially at your age, with the pressures of year 12! It must be a really difficult trying to manage your social life if you're feeling extra anxious. It's totally normal to have these feelings, and for it to drive you inside, and make you not want to be the centre of attention, and I've felt similar things myself.
One idea I have would be to see if you could speak to a psychologist. Sometimes when people have the feelings you describe, they can be having trouble with social anxiety, and a very common and effective treatment is what they call cognitive behavioural therapy (CBT). That sounds serious and a bit crazy but really it's just a way of encouraging you to challenge your negative thoughts using evidence. So at the moment, when faced with a situation, like for example what would happen if you went down the street, your mind might automatically think of all the bad things, like you could trip and fall over and it would be embarrassing, or that everyone might look at you, or some other kind of reason to stay inside. What CBT does is it asks you to challenge those thoughts, and think of how likely those things are to happen, and what other positive things might occur. You might find your favourite snack is on discount at the supermarket, or someone might compliment your new t-shirt. There are good and bad things that can happen, but sometimes our mind just goes straight to the bad stuff!
So maybe talking to someone, like your school psychologist if there is one, or your parents, and they could chat to you about it a bit more.
Either way, thanks heaps for posting, and I'll be here if you want to chat some more :)