I find it difficult when others out you. That's what usually happens to me, otherwise the person wouldn't know in most cases.
You really can't control people and people, for some reason, end up telling others. You can ask them not to, but I think that's about it.
Although it's not good, I think it's human nature to want to tell something, especially if it's something different than what's considered the norm. That happens with a lot of different things about people, from who they are dating, to if they have cancer, or if they are pregnant. News spreads fast.
So, being stuck in the middle of it can be hard and difficult. Because I'm still connected to people who've known me in the past and outted me in the past, I have been open when people have asked. It can get annoying at times, although these days I don't get it as much. My roommies, know, for example - and they didn't know before. They knew me for 6 months before they found out 'cause some mutual friend (who had known me for several years) mentioned it when we were visiting. I was honest and open, and they thought it was cool... then we went back to being roommates and the topic is rarely brought up.
I think in a way, if people ask me about it, I'd rather let them know the facts from me than from the telephone game. I've gotten pretty good at getting rid of that itch with being open at times. In the past, I've found not talking about it with someone who heard and is itching to know, will sometimes go around and start asking other mutual friends for information often getting dis-information.
I guess, in a way, my openness makes it less of a "big deal" and makes it sound more like something that just happens. I find in my group of friends there isn't as much focus on it and they rarely think about it in regards to me. I haven't really run into any problems over it with my group of friends, who just think it's pretty cool and what I did was "awesome."
Now, if it was in a work place, it's something I don't go around telling 'cause who knows who's getting the information. I had this happen once, after a year of working at a place there was one person who was a friend who ended up working in a different department, and decided to gossip about it. It got around the entire building. It was difficult to deal with that, and it made me very upset. The one good thing, however, is that many people didn't believe his gossip and thought he was BSing like he does half of the time. I played into it like that - that he was just saying BS to come up with conversation. A lot of people knew he was a gossip, and that proceeded what he said about me, so his word was as believable as the Easter Bunny.
I think over time I just learned how to handle different situations really well. Different situations 'cause for different action.
Sometimes inaction is also an action, too. Also, never, ever panic.
Like, say, you're at a store and someone calls you the wrong gender - don't panic, get your stuff, and leave like you would normally. I've known others who have gotten into fights at stores over it, which isn't worth it and actually causes more attention towards you and you'll stick in that persons mind. Stores are often so busy they probably won't remember you if you're just a regular customer. Sometimes the sales clerk will say the wrong gender by accident (I know a lot of pretty women who have been called "sir" -- but remember, some clerks will call everyone sir, no matter the gender). Sometimes, if it's busy, they'll just get all confused on who they are talking to.
Often, these are people who won't see again, or see rarely. Why waste your time with them. Let them forget about you.
Also, looking at someone like they are crazy and blind when they call you the wrong gender can also be affective. Often people will correct and realize they made a mistake. Also, remember, that people who aren't trans get called the wrong gender a lot. I have many male and female friends who get called the wrong gender by a clerk at a store or a stranger -- sometimes friends will slip up 'cause they are thinking of someone else. I've known very manly looking men who have been called "she" and very womanly looking women who get called "he" by accident -- a slip of the tongue. It's different than if someone you know is calling you the wrong gender constantly -- in that case, the best thing would to bring it up with the person. Sometimes talking with the person will make them understand; other times, they aren't worth the friendship.
So, in conclusion: Never panic, and pick your fights. Remember that!
As for your Doctor, Nero, I wouldn't panic and freak out about it. Sometimes that is the best remedy. I'm sure the doctor will meet you and probably dis-regard what the receptionist said. If it becomes a problem, then you may want to talk to the receptionist about it. Or, perhaps, if you're not going to be seeing the doc very often, decide not to make a deal out of it. It's up to you. Just remember that panic always makes it worse.