So, I know you're not supposed to wear a binder while doing physical activity, but I'm worried about not passing, like w the bathrooms and stuff. Is there any way that I can make my chest look more flat in a way that won't hurt me?
I can't say I have a ton of personal experience but you may want to consider looking into a compressive sports bra or a men's athletic compressive shirt (which you'll find in the men's underwear section of most big box stores. Target carries them). Underworks does make a lot of sports bras that many guys have found works great for binding and being active.
Sports bras or sports compression shirts will be your best bet, since binding while working out isn't a good idea.