You don’t fix this because there’s nothing to fix. There’s nothing wrong with you or what you’re doing.
When I write, I metaphorically drop my pants and defecate into my text editor. I know that everything I write is going to be shit at first, and I’ve learned to be OK with that. I can always polish the turd after I’ve gotten it out, but I won’t get anywhere by holding it in.
If you’re rambling, it might be because you need to ramble. If it comes out disorganized and “awful”, it might just be because you’re not used to writing. The only way to get better at it is to do it poorly at first.
Be patient with yourself. Try not to compare yourself to people who are farther along in their respective journeys than you are in yours. Take your time. You’ll get there.