That is weird to only have one for the class. We all have, and/or are, individual mentors.
The thing about the head down, mouth shut... made me laugh. In my case, it's true. I to stood up for myself a couple of times...not pushy, but my clinical instructor didn't like hearing that I may actually be right and she may have to alter HER thought processes. (Of COURSE those weren't words that actually came out of my mouth!!!!!) I was always gentle with it, too. My eyebrows raised and starting, sounding almost apologetic, with the phrases like, "Um. Can you help me? I'm not sure but what would happen if...?" --VERY passive aggressive. Still, when I decided to shut up and cover my a$$ if necessary, we got along SMASHINGLY!!!
I think as long as you know your stuff, you'll be ok.