yes, starting a new job is always a learning curve; everyone feels nervous. Once you've got on top of that, you'll find that having done so boosts your confidence.
I've always thought the words of The King and I got it right:
While shivering in my shoes
I strike a careless pose
And whistle a happy tune
And no one ever knows
I'm afraid.
The result of this deception
Is very strange to tell
For when I fool the people
I fear I fool myself as well!
Not so much a matter of 'fooling yourself', perhaps, but if you seem confident people will assume you are confident and they'll be happy and that will make you happy - problem solved. Just don't fret if it takes a while