I need to get a job, but I'm shy, scared of everything, and have pretty much zero confidence. What to do?

I'm 18 and just started college cles. I need to get a job, but with the way I am, I feel like I'll never get one, or if I do, I feel like I'll be horrible at it and constantly making mistakes and will get fired or something. I actually did manage to go to one store last summer and ask for an application, and they gave me one, but never ended up calling me back, so either they just decided they weren't hiring, or they got the impression that I was shy and nervous and didn't want me. I'm not sure which it was. But now I really need to get a job. I'm just so afraid though. I just know I'd screw up a job interview, because of course I'm going to be nervous. And when I'm nervous I always end up stuttering or saying something stupid, and my body starts shaking. I can just picture being asked a question that catches me off guard, and I'd just sit there blathering like an idiot, or I would just not even know what to say. And if I did manage to get a job because by some miracle, the manager didn't get the impression that I'm a complete nutjob, I'd still be nervous and I'd just be petrified that I'd make mistakes and be humiliated in front of a bunch of people, or make the manager really mad. And I pretty much have to get a job in a store or in a restaurant where I'd work behind the counter, and I'm really not good at figuring out how to do manual things like that (like working at the cash register). I just don't know what to do. Sometime in the next few days I have to start going to places to see if they're hiring and get applications, and I know you have to present yourself to the manager as confident, and I just know that no matter how much I try, I'm NOT going to come across that way, because I'm NOT confident at all, I'm just a nervous wreck. I hate that I am like this, and I know it's probably going to ruin my life if I can't stop being this way. How do I not be so nervous and afraid?