Scared about starting a new job

I start a new job on Wednesday and it something in which I have to deal with the public. It took me awhile to find a job that I could apply for and actually get hired. I'm very worried about dealing with the public, and the more I think about this job and the closer it gets to Wednesday, the more I start to freak out. I also have anxiety issues and this is probably the worst type of job for me I know, but does anyone have some advice or tips as to how to deal with something like this. I'm worried not only for my anxiety but my depression as well, I'm a very sad and quite person and I know I need to pretend to be happy and outgoing, which is most likely going to be the hardest thing for me.