I haven't even begun transition, so I have no experience to speak from. Take what I'm about to say for what it's worth with that in mind.
My instinct is to tell you to forget about whether you "pass" or not. You are who you are, introduce yourself as such. I think it's generally true that people will take a cue from you. If you are comfortable and nonchalant about who you are, most of them will be too. The ones that aren't, I doubt you want to associate with.
Also, you don't have to introduce your gender. I've never once heard someone say "Hey, I'm Jason and I'm a guy!" Just introduce yourself, let assumptions fall where they may, and correct the incorrect ones if that's something you want to do. If someone says she, just gently correct them and leave it at that. If they decide they want to press and ask questions, you can decide how to handle it then.
Easier said than done, maybe, but I really do think the less of an issue you make out of it, the less of an issue it will be for others. Sure, there might be people who would take issue with you because of their own biases, but those people were never going to be people you want to associate with anyway. Just be safe, if you feel threatened don't ignore it, talk to someone who can help ensure your safety.