Nervous about meeting people from the internet?

Ive been invited to the pub and meet up with some people i met over the internet. but im really nervous, and scared. they might have expectations and stuff, im a lot different in person, im really quiet at first etc... then if i make a fool of myself, theyll probably not want to bother with me again. plus im only 17, so i wont get served for drinks, not that i intened to plastered or anything, but one of those will probably have to buys me one, and id feel stupid. i just over think little things, and get freaked out. /= what woudl u do?