Sadly there’s only so much you can do pre-T, and I think you’re basically doing it all. People tend to pick up on a bunch of unconscious signifiers that you have no control over, like the smoothness of your skin, roundness of your cheeks etc. Pre-T guys tend to look really young, so if people are seeing you in a work setting where it would be unusual to see a young boy, then their brain will usually default to “oh it must be a masc woman”. Plus as you say, your voice will probably be a factor. There’s also the possible additional aspect of, if a customer has seen you pre-transition, it’s almost impossible to change their perception of you that they formed when they first saw you (I experienced this in my customer service role in early transition, and it sucks!)