How do i show more confidence in my new job?

i've just started a new job today as a activities organizer in a nursing home, i know i can do this job and in my interview i was really confident as it was one to one. but when i've started today and we was in a massive group i totally clammed up why? i need to get over this asap because my job is all about confidence, ive been out of work for a while before this job, if any one could give me any advice i would be very grateful :)