I used to despise mirrors, because whenever I looked in them they showed me a pretty girl. But over time I adjusted my mindset and now to me I look a perfectly ordinary boy, despite the round face and breasts. I sort of conditioned myself to associate my features with masculinity, in order to hate myself less. The only problem with this is that now I don't try to pass at all because I consider myself sufficiently masculine already - which in actual fact is not the case, as I'm pre-T and don't own a proper binder or anything. Therefore I get 'miss'd and 'young lady'd and men hold doors open for me excessively. This causes bad dysphoria. So what to do? Where can one find the golden line between being too critical of oneself and not being critical enough?

It's great you've found a way to be OK with your appearance. I suppose though that doesn't stop you from maybe changing aspects of your clothing and hair etc if you haven't already. If you're not binding perhaps wearing a small tee under a baggy shirt. I'm sure the guys will have some useful tips.

I guess I kinda feel you, in the sense that since I've started binding I've noticed that I tend to walk with my chest out like all I have there are my pecs. My chest looks like I have decently sized pecs which is cool but until the rest of my body catches up in "size" I think it probably looks odd. I catch myself walking the way I do and have to remind myself to be a little more conspicuous about it, especially since I don't/not really trying to pass right now. My roommate made me realize this when she told me it was funny how I tend to show off my "flat" chest while her other trans friend actively tries to hide it. I'm kinda jealous of how flat that person looks actually..

But anyways, getting a binder/wearing baggy clothing might help. Though really, I think your confidence and the way you carry yourself can say so much on their own. It's great that you can feel comfortable with yourself though, I think that's a great step towards passing in its own right.

I think it's a hard balance, trying to be OK with your body as it is, and accept it as a male body (though an atypical one), but also recognizing that most people are going to gender you based on your appearance.  The unfortunate fact is that, if you want your gender identity to be recognized and supported by the people around you, you need to either surround yourself with people who will respect your stated gender no matter how you look, or change how you look to match people's expectations.  It's very difficult (usually impossible) to interact only with people who will honor your gender regardless of your appearance.  In a perfect world, social gender would be defined solely by the way we identify.  But this isn't that world, unfortunately, and in the world we live in, if we want to be treated as male we need to look like men. 

Don't know what to tell you. Sounds like you've managed to conquer the body dysphoria, but the social dysphoria is still a big problem for you.  You can either learn to accept misgendering the way you've learned to accept your body, or take steps to change your appearance so that you're recognized as male, even if you don't pass 100% as cis.