Remember, everyone on that inverview panel will have at where you are, and in far more hostile circumstances - in order to get to their current position, so they know exactly how you feel.
The purpose of the exercise is to find someone to fill the advertised post, so that's what they are looking for - not to trip you up and make you feel uncomfortable.
You have been selected for an interview - that means you have already passed a 'paper sift', and means they think you are worth their time to meet and talk to.
For those reasons, be confident that you stand a good chance.
As far as 'being yourself' - that's not the idea, so don't worry about it - it is an artifical situation and everyone knows that, so if you stay relaxed and think about your answers, you will do just fine.
Interviews are like hang gliding - it feels far more scary thinking about it than when you actually come to do it.
No-one is going to die - the worst that will happen is that you are unsuccessful, which leaves you where you are now - nothing lost - experienced gained.
You have nothing to lose - go for it - and let us know!