Is this considered a big mistake while working at McDonalds?

Oh, Angel, you had a bad night. Well technically he could have fired you for leaving the till, the other stuff is just part of the learning process. You have to make the effort to learn the job and since you took responsibility for your mistakes, that is a big plus for you. You are already on drive thru, so that must mean you are good, since you should still be on counter. Chin up, it gets better.