no confidence helpless...

I'm 21 years old and started a new job 5 weeks ago as a receptionist .. I'm normally shy around strangers I have very little confidence so whenever im put on the spot I don't do as expected. I know my lack of confidence shows .. I just feel so helpless I still try but I don't do everything right & when I leave work knowing I messed up I feel terrible. I don't want to go to work but of course it's a necessity. I don't want to get fired .. Everything I do requires confidence since I have to communicate a lot with strangers and my managers, who make me nervous. I don't know what I can do to help boost my confidence..