Be confident, just fake it haha. Salons need to have a good image, so what they care about is that you make an effort with your hair and makeup and that you have an outgoing, personable attitude. So just act happy and smile a lot. Act friendly and outgoing, even if you're nervous. Just pretend you're not. Focus on the interviewer instead of yourself and you'll stop feeling so self conscious. Pretend you are interviewing them instead.