I will say that you're not the first trans person I've spoken to, both here and in my personal life, to struggle with more general body image issues on top of dysphoria. It's such a crappy combo, and I'm sorry you're dealing with it.
I'm glad you've been able to schedule a visit with a dietician, though the "are they trans competent" roulette is never fun. If you're suspecting some of the eating habits are arising from a need to punish yourself, do you have a more general mental healthcare provider you could talk to about that? I do also want to give you this resource: https://www.transfolxfightingeds.com/
. It's by and for trans folks dealing with eating disorders, but it looks like some of the resources in it could be really helpful for you.
You mention that some part of you already knows that the expectations you're putting on your body are normative and unhelpful. Do you think there are certain ways of challenging those norms or negative messages that might be helpful to you?