It's cool to be nervous. I was nervous to meet my boyfriend's parents the first time, but if you don't meet them soon, you will have to meet them later on, so basically you'll be screwed either way. It's totally worth it though, because it makes your girlfriend's parents aware of what kind of person you really are, which is very important and you get used to their parents so quick. They're not aliens that will suck your brains out, so don't worry.
Yes. just act polite. And show them about much you care for her! Let them know you will not let anyone hurt her! but be yourself, but be crazy though. Just be calm, maybe ask your girlfriend if there is anything you should worry about.