First job tomorrow but i'm scared!?

I"ve never worked and im afraid i'll screw so many times on something. I feel so stupid and plus im very forgetful like i forget almost everything and it sucks. Im 20 and for some reason im scared. Im working at subway but its a fast paced job but the problem is im a slow worker everything, even in school. Im supposed to be working the cash register tomorrow but im terrible math like so so bad so im scared about that and cooking and getting everything done quickly is gonna be even harder for me. I so stressed out right now just thinking about this. I mean what if i get yelled at because i can't complete a job on time and even doing right. I also have ADD which is problem. My parents said i have to work sooner or later but i terrified and i feel like im gonna pass out. I have social anxiety too. The say that i'm dumb, stupid, waste of time, worthless, lazy, and my brother calls me a bum and then tells me t grow up. My dad says that im irresponsible. I feel horrible about tomorrow and about myself. What do i do?