Use the men's restroom. No one cares. I feel like most FTMs put too much stock into it. Pre-T I went to the men's restroom and no one questioned me. I live in TN, and I can guarantee you that the homophobia and transphobia(many dont even KNOW there are FTMs in the world)here is pretty much unmatched.
I swear to you that guys don't really look at other dudes well enough while theyre in there to even NOTICE. In fact, I never look at ANYONES face. I basically just see shadows.. I don't pay attention, because like everyone else, I just want to piss and gtfo