I'm sorry! Try not to let people get to you like that! You don't have to win any arguments because you don't need anyone's permission. You don't need their acceptance or support if they don't actually have any to offer. There is a world of folks out there who will accept you.

I know how hard it is to feel secure enough to be the source of your own affirmation early on but do try to find it within yourself. If you can't find that security, then let go of the need for it and just follow your heart. We are all winging it through life anyway, so go ahead with the DIY. Keep it somewhere safe at your university or at a friend's place in a lockbox. You said, "no one spoke with me about it ever." If you don't have trans friends in your life yet, go find some at those organizations you mentioned. The trans organization in my city has lockers available for people with problematic parents.

If you feel like you have to self-harm again, try to put it off for a little while. You can always do that later, right? Try to put the sharp thing away too. If you can't quit thinking about self-harming, try instead to let the thoughts pass by without interacting with them. Just breath, let the thought come, and let the thought go. There's enough suffering in that moment, so just be with it.

By the way, the whole nature isn't queer thing was a total cover-up. The old explorers knew nature was queer as fuck and hid the information to deliberately create ignorance. Now we have to deal with their mess hundreds of years later.