If you want to improve on it read the The Mental Game of Poker, they are good for it. I don't do much, but learnt that it's only a game, and if I'm loosing money (not actually because I made then from freerolls) it was part of my choice not to manage my bankroll better.
Fake it till you make it, when you play enough you will get more confident. Until then work through the rough parts and understand everyone doubts themselves sooner or later.
