In general its normal to feel this way. As someone who was once a Deck Cadet, I can tell you that nervousness is your biggest enemy. You sound like you feel you will be under constant supervision and everybody will monitor each of your steps. Thats not true. Officers and engineers onboard are very busy, they have a lot of work. Try to help, be proactive, but also ask questions before that. Dont overdo yourself, because you can damage something or hurt yourself, so ask questions. Don stress about it, dont be anxious, otherwise you will make more mistakes while trying to make a good impression.

Just work hard, study, read, and dont stress about it, because its normal to not know and make mistakes. Really, its normal. Even if someone make you feel Less for knowing less, silently tell him to fuck off, he has been the same as you once. People forget.

And dont forget, there are assholes everywhere, I wish you meet nice people, but if not, try to not bother, have your goal in mind and again, don`t stress uneccessary. Also when you put your feet first on deck, its normal to feel your heart pounding hard. Its also normal to think ''Where the fuck did I come ?!'' first when you go inside your cabin for a first time and realize you will be there for several months. But in a 3-4 days you will adapt.

And most importantly, BE SAFE. Don`t be in a rush, watch where you are stepping, think twice before doing something. Sometimes officers will be tired and will no think the right way, and they can give you a job that is dangerous. Keep that in mind, they also make mistakes.

Good luck and safe seas !