I think it's safe to say that most crossfit gyms are accepting of LGBT people, and that most people who do crossfit are straight.
Also, I've never experienced flirting or hookups or much talk about dating/relationships at a crossfit gym (haven't sought them out, and wear a wedding band so maybe I just missed them) so even if there are queer people and you aren't, you wouldn't really have any way to know and it wouldn't matter to the workout.
If you are incredibly afraid of being in the same room as gay people you should probably work on that before physical fitness because I imagine it's very limiting. But other than that, give crossfit a try!