Terminological quibbling: sex is not gender.
"Sex"--i.e., biological sex--is generally fairly binary. While it may be a bit of an oversimplification, a male/female dicohotomy accounts for almost everyone if we're only looking at biological sex. Yes, there are some individuals who are hermaphroditic or for whom their sex is unclear, medically (not "I can't instantly tell by looking at them), but male/female generally works here.
"Gender," though, is how people self-identify. Gender refers to a cultural categorization of individuals based on their actions--manner of dress, language, etc--and, yes, often their biological sex. Unlike biological sex, a simple male/female dichotomy just doesn't work here. Some people identify as absolutely, super-duper, all the way male. Some people identify as just regular male. Some people identify as neutral/neither. Some people identify as a third gender. It doesn't strictly need to correlate with their biological sex (see, for instance, the existence of transgendered people, whose gender does not match their biological sex). Gender is an individual trait much like what food or music you like, and because it's an individual psychological/personality/etc trait, it's as variable as people themselves are. So there aren't just 64 genders--there are literally an infinite number of genders. Well, an infinite number of ways someone can identify their gender--as very masculine to very feminine and everything in between (and anything off of that two-pole spectrum), with the parameters for masculine/feminine/etc varying across different cultures. Being a continuous spectrum rather than a binary "male XOR female" situation, there are infinite ways someone can identify their genders.
So, no, there are not two, because gender =/= biological sex.