I haven't got past it yet, I have the same problem, I practice my voice but since I'm not full-time I have to switch back to male voice and that seems to throw it off.
I've come out to a few people so that I can use my fem voice with them but they've known me before and think it's weird so I often revert to male without thinking.
If your problem is switching context like me, then I think the only way to keep it female is to always use a female voice no matter what, with everyone. If your full-time that is.
I think that's the only way to get past it.. it's hard work too at the start. I didn't find finding my fem voice very hard, but sticking with it everyday and being able to instantly get it back is the hard part.. it just takes time like anything.