I want to be a Femboy but I don't know if it is a sin so please answer my question.

What you sinabi to do is good, but it won't keep you saved. First off, regarding the original tanong you answered no to, wanting to be a femboy in itself is a kind of lusting for any number of things: friends, attention, acceptance, some for sexual attention, etc. Regarding you sinabi about how to stay holy, if you don't communicate with God, hear his voice; have an actual relationship with him, you are most likely still living in sin. Plenty of people go to church, keep their face and hands clean, smile with their chin up; they think they have the pag-ibig of God in their puso because they are nice to other people. But, inside of them is penned up sin that they stuff up that they know their flesh wants to get loose, and they commit sins in their puso and mind. These all should be repented for. Many get baptized in water but don't truly mean it. They think because they are dunked they have his blessing and don't understand the Spiritual meaning. You must be truly baptized, (have no unrepented for or unconfessed sin, die in your sin, kill your flesh, and rise up in Christ) to receive the Holy Spirit; and you will know if and when you have received it. It is not just pagganap happy and ipinapakita to everyone that you are so nice.