It's harder being a girl liking this kind of stuff, believe me.  
Only because according to popular stereotypes you're a mythical creature. Popular culture at large hasn't caught up to the explosion of women into geek culture that has happened over the last 15 years. Starting with anime and games but now encompassing pretty much all of nerdom. This is why you still have shows such as 
The Big Bang Theory making jokes like "Women? Who read comics? Pshaw!"
Of course the prevalence of insecure testosterone fueled 12 year olds, and 30 year olds who act like 12 year olds, on the wretched hive of scum and villainy that is Xbox Live also discourages women from being open about their gender. A culture where boys/men who don't have the balls to do catcalls in real life (or even talk to a girl) show each other how manly they are by sexual harassment over a headset. 
Not to mention the fact that a not-insignificant portion of the male population in nerd culture blames 
women for their inability to attract the mate they feel they're entitled to. And like other misogynists have decided as a result that all women are out to trick and manipulate them. This is where you get the uproar over "fake nerd girls" it's like "What? A woman who likes the same things I like?! This cannot be, I cast you out vile temptress!"
I think the best way for nerdy women to reverse this stereotype though is to just keep doing what you're doing. Be comfortable and be yourself. Guys who dress up as superheroes aren't grilled on the history of the character so if you cosplay or wear a nerdy shirt you don't have to prove shit to anyone, if some guy says you need a quiz to prove you're a "real fan" and you don't want to bother disproving him just tell him to get bent or ignore him. Eventually people will catch on that not only do you actually exist, but that nerdy women like you are not as rare as they used to think.
PS - 
I do think there are 
some women who pretend to like things they don't because nerd culture is/has recently been "fashionable" (or maybe because they're an actress and the nerd market is the niche they've found) but here's the thing - 
there are lots of guys doing the exact same thing probably more of them in fact, and they don't get 1/1000th the shit and accusations that women do. If a guy says he's trying to get into comics or whatever it's like "Welcome to the club brother!" while a woman might get asked "Why are you doing this? What are you up to?" Nerdy Guys, the prevalence of the boys club mentality reflects poorly on all of us and it needs to stop.