<human>: Can you provide a brief overview of the text?

My coworker is a transwoman (assigned male at birth, transitioned to female) and to be blunt, she does not pass very well. She is aware of this, but I use her preferred pronouns, as thats what she has asked. We're friends outside of work and honestly I've just gotten used to saying "she" and "her" because to me, she's...her. Who cares if she looks "manly", she can go by whatever she wants. 

We recently hired a bunch of young white dudes. They all sit together in the office (open office environment). While talking to one, I mentioned her name (which is rather agender) and then said "she". The coworker got confused and didn't know who I was talking about. I had to say I used her preferred pronouns, and pointed out she sometimes sat near them. They got an "Ohhhh" look on their face and he thanked me for telling him. 

Later, I saw them all talking, raising their eye brows and looking around in shock. They were pointing to where she normally sits and all looked surprised. I told them "If you're talking about what I think you're talking about, don't even worry about it guys and don't be weird".

I can't tell if they are just genuinely amazed/shocked or if they were making fun of her. I realized maybe I should have kept my mouth shut, because transwomen are so often hurt, I'm now scared I may have put her in danger. I didn't mean for it to become office drama or gossip. 

I know I need to tell her I outed her, I feel like a piece of shit, but I don't know what to do or how to handle them if they begin acting aggressively towards her. We're a small company and we don't really have an HR department. What do I do?
<bot>: Accidentally outed my trans coworker, now worried she might get hurt or be made fun of and I don't know what to do. Do I talk to our (rather pathetic) HR person?