busy work and pregnant

I'm 5 weeks now with my first. December 10th I have to work that day(work in a restaurant) and it's going to be extremely busy because our town has a Victorian walk. They'll have extra girls working that night but it'll still be busy. And it can get a little stressful as it is when I'm busy by myself. So I'm a little worried I'll get too stressed and since I'll still be early in pregnancy. So what should I do? I can't really tell them I can't, I mean I can but idk if they'd fire me if I did that. And I want to work that night I'm just a little worried I'll get a little too stressed and something will happen to the baby. I plan on asking my doctor about it to when I have my appointment.