It's very unrealistic to expect to feel immediately in your comfort zone when you're literally in a new place where you don't know what you're doing yet. It's normal to feel a bit discombobulated when starting a new job, but the good news is that it passes as you start to get the hang of the role. One shift (or even two or three) isn't enough time for that to happen, though.
Even if you don't need the money, I would encourage you to stick with the job, because that having-a-new-job-and-feeling-all-at-sea feeling is something you'll meet again in the future, even when it comes to whatever career you seek in the long term, so learning how to deal with it now is all to the good. And if you do need the money, definitely stick with it - chances are, if you ditch this job and find another one, you'll feel just the same there (by which time the newbie feeling would be wearing off if you'd just stayed put in your current job).