I do d&d writing too, but never that much, as I fear what happened to you would happen to me, jumper. however, I always like, write down the general idea of what I want, but let the players go ham, that way I can't get disappointed when they railroad their way into hell and back.
actually had a really cool first time DMing during the beginning of quarantine, turns out my players liked my campaign a bunch, now they want me to DM another. I was doing a horror based one that I had planned for quite a bit. it was relatively short but i'd love to expand on it.
That was sort of how I got my first campaign idea going, It began as a really rough idea of a plot that I ran for a group of 4, they said they liked it, but I could tell that my inexperience as a DM really marred their fun. The story was just something I thought was interesting, and I believed I could sort of 'wing it' from there. However shortly into the session I realized that style of DMing is really solely for well-versed Masters. I had the maps that I needed, the NPC's, but not a solid overarching plot that I could latch on to in case I got lost. I just had the hook, and nothing else. That and I ended the session with a semi-long exposition dump, that I'm sure bored them a bit. Now after a few years, I got a sudden idea that could tie all of it together into a solid cohesive unit, a world that could be as interesting as it was bleak, and I went on from there. Creating the synopsis, the gods, the rough idea of the beginning, middle, and end. And the first town as a sort of 'demo' for the first session.
Sadly, my first and second tries of running that campaign didn't turn out well. I ignored a lot of red flags out of over-eagerness for my idea. I had gotten a lot of praise for my concepts and it made me a bit too bold in attempting to execute a session to try out my 'demo'. If there's one or two tips I can give you to avoid disaster sessions, LISTEN TO YOUR GUT, if what you're looking at is something you THINK is a red flag, (whether it be one player or multiple) it is a red flag. And it should be dealt with immediately. If you're going to host online with strangers, vet them thoroughly, so you don't get the dreaded ninja-scalie. And lastly, don't over-plan your sessions, people can be chaotic, but I'm sure you already know that since you've hosted already in the past. Plan out the plots for your quests, hooks, characters, and checks, but don't write it out like a play, the PC's are going to want to do some crazy stuff.