Thank you for your service to your country. I joined in '71. I put in for ET. I scored high on all the aptitude tests, so they made me an EM. That is what they were short of, so that is what I got. No good deed goes unpunished. Of course, that was 40+ years ago, so some things may have changed.
Your first task is to get through basic training. It can be daunting, but don't get discouraged. The real navy is much different and better (don't laugh, you ex-squids, I speaking relatively). Just grit your teeth, do what you are told, and don't try to make sense of it. there are a lot of intellectually challenged in this phase of the military.
After basic is A school which is a snap. Then Nuke school, which with your science background should also be a breeze. You will learn a lot of good info, most of which will apply specifically to the navy. You will have to do things the navy way and there is close to zero tolerance to stray from the path. Follow procedures, obey orders, and you'll do okay. When you get out and take a commercial nuclear job, they expect the same.