Unfortunately this is another one of those things that takes time and practice. Right now I do the best I can and just accept that my male resonance more often than not comes through. Other times my voice probably sounds fake and people know I'm pushing my voice up. However, at the end of the day, I just don't care. I've accepted that this is part of the process. It actually helps that I know I'm easily clocked right now anyway. People can figure out I'm trans pretty quickly so if they figure out my voice is not real, then who cares really.
What I've been doing is practicing as much as I can whenever. Driving alone in the car on 30-60 minute trips is a great time for this. I record myself from time to time as well and use that to figure out what I need to improve or to remember what I did that sounded good. I also try to sing with a female voice whenever I can (again this works really well in the car).
I have a deep baritone natural voice. It's very chesty and booms. Right now I'm trying to practice getting it out of my chest and softening my tone without getting squeaky or minnie-mouse-ish. I've had varying success, but it is getting better. I start voice therapy in 2 weeks, so that should really help as well, at least I hope.