Dominick, I used to be like you in middle school about everything. I wouldn't stand up for myself no matter what. But one day I just got tired of the bullsh** and said my opinions no matter what. Not in a snobby way or anything, just to stand my ground.
Know what I found? People don't actually care if you stand up to them. If anything they thought I was a better, stronger person for standing up for myself, one that deserved respect. And from then on, I indeed was respected, people even describe me as OVER opinionated sometimes. And I learn after you stand up the first time, it gets easier to do it from then on. Sometimes I still lay low, but nothing like I used to.
I rambled, I know...Moral of the story is that people respect you for being confident, so go tell that nurse with a clear voice, "I'm a guy, please refer to me as one."