I have recently started a new job?

I have recently started a new job and was asked to help at another store as well as my base. I accepted, as I have always been the type of person to do what helps others in whatever way I can (even if it doesn't suit me). Since the first day I went in I did not like it at all. I feel very intimidated and uncomfortable, as the workers make it that way. I have had my fair share of nasty colleagues, but I don't want put myself through it. How can I tell my boss I do not want to go back there and am happy to be staying where I originally was? I dread walking into the place in fear of making a mistake or doing something wrong.