Yeah I kinda know how you feel. I'm always paranoid I did or didn't do something. I'm guessing by your age this could be your first job? All I could say is be the best you can be and you should be able to live with yourself. Good luck!
I am the same way, second-guessing everything I do and basically being paranoid about it. I just got a job as a busser and i find it pretty anxiety-provoking b/c im constantly wondering if im saying the right things to the guests/coworkers, whether im doing things the right way, every little thing i do im doubting myself..
Its hard but i think we have to lighten up and realize everyone learns by making mistakes, big or small, and the little things we obsess over go mostly unnoticed to other people.
My co-workers bro had the same problem. Whenever someone asked him to do something, he would repeat it back again every single time. For example if the manager asked him to make a photocopy, my co-worker's bro would be like, "So you want me to make a photocopy of this?" Then eventually the manager was getting irritated and told him to just do what is asked.
The morale of the story, just use your instincts. Only ask questions on stuff you feel really need to be addressed and not every single question (Not that I am assume you do that). I think you will be fine, just learn at my co-workers bro expense lol.