Relax, OP. They wouldn't have hired you if they didn't think you could do it.

It's very common to feel nervous in a new job. Everyone has had (and usually hates) the experience of being the new kid, having to ramp up etc. Just accept it. Take people to lunch or coffee. Give yourself "on-boarding" time and do get-to-know you meetings of 1/2 an hour with teammates. Ask them about their jobs, ask for pointers.
Also realize, it's going to be several months at least before it feels like old hat.

Lastly, spread around your questions. Esp. in the beginning, when you're in meetings, just take notes and then look up the answers or ask people privately afterward to explain things in more detail. You have a grace period for a little while as a newbie--just use it to ask questions and learn more.

I am a federal attorney. I just accepted a position at another agency. I will be practicing the same area of law, but for an entirely different type of agency. The new position seems to be an ideal fit for me, but I am giving up a lot in terms of the contacts I have made at my current job and the level of subject matter expertise I have accrued. While the law is the same, I will be starting from scratch on getting to know the people and the mission at the new agency. I'm extremely nervous. Does anybody have any stories to share about successful moves like mine?
Thanks!