I was really nervous for the first 6 hours ish about just being in the air. I was worried that I would never be able to solo because of it, but just over 3 hours later I kicked out my instructor and went.
When I first got my PPL I'd double or triple check my route, the wind, the weather, the fuel, the oil... but now I'm getting more confident in myself. I have to say that the best thing for my confidence was to get up in an aircraft with a fair bit of kick, and do some aeros. A spin was demonstrated to me while I was doing my PPL, but I'd been pretty shook up by it (I was only on my 5th hour, and still worried about the height thing!). By the end of the aerobatics I was loving it though, and really really
really want to go back and do more! The second best thing for my confidence was flying the Chipmunk.
When I got back into the C152 after both those I noticed my general flying had improved beyond measure.
Confidence comes with competence, and competence comes with practice.