Way 1 · best default
I'm a bit nervous
Honest and calm. Safe to say to anyone, even your boss or an interviewer.
Examples
I'm a bit nervous about the presentation, but I've practised a lot.
Sorry, I'm a bit nervous. It's my first time driving on the motorway.
In a conversation
A: Big day tomorrow. How are you feeling?
B: I'm a bit nervous, but I think I'm ready.