I find that passing is all about confidence regardless of anything else.
Anxiety is just a fear ( sometime irrational, sometimes not ). Although anxiety comes first, it's what
is before confidence. I remember the days before I found my confidence. I didn't pass, which gave me huge amounts of anxiety. But I've never let anxiety stop me. 99 times out of 100, the fear behind it is baseless. And so what anyway? I wasn't going to stop being the authentic me. And so confidence grew every time I pushed anxiety away.
Having said that, my confidence was shattered with one particular public and embarrassing event some time ago. It was shattered because I started denying and repressing being trans. It turned from a fact into a weapon, which when called out ripped me to shreds. I've learned a lot from that, and learned to own being trans as much as anything else. Then it's not something that can hurt me.
Now days, I've no idea how other people perceive me. I just go about my way and don't really take notice. There are no issues when chatting to anyone or doing anything. I occasionally notice guys checking me out, but otherwise I'm basically ignored ( which is just perfect ). I believe this is just blending in, which has always been my goal. But I've also little to be anxious about ( I think ). While I am tall at 6", my body is mildly feminine, and my voice is good. I don't just talk the talk

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So if you get anxiety over your voice which you know isn't where it needs to be, then invest and fix it ( I'm suggesting therapy, not surgery ). You're going to need your voice for the rest of your life, so invest...

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If you get anxiety over things like height ( which you're not tall compared ), then you're going to have to learn to deal with it. Anxiety over something you cannot change doesn't have much purpose. Remind yourself of that every time, and soon it will just be, and it won't bother you as it does now.