I am in the lgbt community. I am not lgbt myself, but I'm in the community. I've never met someone who thought there were more than two genders. All these classifications are not genders. They're just that. Classifications. Agender? That's not a third gender, it's the lack of gender. Transgender? That's just being the opposite gender of what you were assigned to at birth. Gender fluid? That's just constantly switching between the two. None of these are third genders. If I give you the choice between two flavors of ice cream and you decide to take neither, are you getting a third flavor? How about if I give you a flavor and you decide that you want the other one? How about if you can't make up your mind and keep switching between the two? None of this involves a third flavor.
Let me break it down for you: there's two genders, nothing more or nothing less. The one you were born with is the one you will stay for the rest of your life, no matter what prefixes you put in front or what kind of clothes you wear or anything.