What you are describing sounds normal to me for a busy fast food place (I worked at one that was really, really busy!) If you stick with it you will become better adjusted to the pace and start to notice you will get many of the same customers. You should also be able to talk to your manager and say you're feeling nervous and you want to do a good job and not to mess up. She or he may be able to offer some pointers or tell you to observe a more seasoned worker for tips on how to interact with customers. Hang in there! Courage!