Hannah's spot on Jess. You just need to know the right things to say, play up your strengths to the maximum and employ some blagging tactics for the few bits you're not that sure of.
Honestly, you're clearly dead smart and even if a job looks fabulous but terrifying and you have doubts about your abilities - you WILL be able to do it. A bit of research before an interview and you'll walk it.
IMO everyone who is any good doubts themselves, its those that think they know it all already who are the folks that do a bad job. I've had 3 big promotions since I started with this company 7 years ago and every time I went for one I felt out of my depth.
Then when I got the jobs I was terrified I wouldn't be able to do it.
Some days I still struggle to believe the job I've ended up in. I keep expecting someone to catch me out and send me off to do the filing instead!
You'll do great whatever you choose to do. Like Nikki said, you've got everything in your favour, you just need to see what other people see in you and for those bits you're not confident about - pretend you are! xx