Keep your doubts to yourself. An interview is centered on the subject you know best - yourself. Don't let rejection erode your confidence. The interviewer knows less about you than you do. Don't let the advice of others shake your confidence in yourself.
Interviewers expect a certain amount of nervousness.
Try to avoid sweaty palms by sitting with your palms exposed to air. Look at the down side - before the interview you didn't have an offer. The worst that can happen is that after the interview you still don't have an offer. Combat nervousness by relaxing your muscles and getting enough sleep. Don't worry about failure.