I got "Good night Gentlemen" last night at work, since I was working with a guy. I just laughed. He wasn't out to get me, he just misspoke, and it was more embarrassing for him than it was for me because I'm pretty comfortable where I sit. I just thought I'd share that story as it relates to this one.
Dude is pretty genderless, especially amongst my generation or younger. And I say "you guys" all the time.
In the event that someone does mis-represent your gender to you, just laugh. It's not you who should be embarrassed. They are the ones who committed the error.
Does not matter, need not be.