ok, let me tell you something
EVERYONE is scared of what OTHER people will think. That other people will judge them.
It's just that some people take the plunge (the "confident" people) and others don't risk it.
If you start up a convo with someone first, they will appreciate your effort, because in any social situation, if ur meetin new people etc, it is always daunting.
you just have to jump in. Take a risk.
Start off by talkin to one person or two...don't go to a group and introduce yourself. lol that is extremely hard.
Gradually, you'll become less scared. Seriously, everyone is scared of what everyone will think. So, just because someone looks confident, it doesn't mean that they find it really easy...it's just that they're willing enough to jump in.
And the more you do it, the easier it becomes.
and for presentations...when ur presenting, just look at the wall...looking across the wall horizontally, "looks" as if ur lookin at everyone in the room, but really you're not. Gradually, you will get more confident and will actually look at the people.
Also, everyone gets nervous about a presentation too....i mean, get to uni, and you will have to present in front of packed lecture halls! it's daunting, but get so involved about ur presentation, that it wouldnt matter how many people were watching.
just remember that everyone is scared and most people will appreciate the fact that you're trying. and noone will judge you in the wrog way.
Good Luck!