1) Unless you are considering surgical or hormonal modification, there is no reason you can't change your mind later - though it does get confusing to others, that's far less important than your comfort.
2) It's okay to be in a socially in-between state. There are other identifications, such as http://en.wikipedia.org/wiki/Genderqueer
This is really more a matter of preference than a problem that can be solved through logic.
Our society is not very accepting of people who don't fit into gender roles. Hormonal modification is necessary to "pass". Also, hormonal modification is much more effective the earlier you start.
If it's worth saying, but not worth its own post, even in Discussion, it goes here.