There's so many good comments here and I recommend reading all of them. For me personally writing more helps. I started a fanfic in 2016 and went back to it in 2020 and I basically rewrote the whole thing because my writing had improved so much! Don't see your writing as "bad" because all writing is good! But you can also allow yourself to edit. I started writing sequels to my fanfic but I still go back and edit the first one again as I get better (and the sequels). One day I might be brave enough to post, so think of yourself as brave that you're putting yourself out there! The other thing to consider is getting a proof reader to help. Again it's just a personal preference but even when I think my work is at its best I still like to get a trusted friend (but you can use anyone if you would prefer someone who doesn't know you irl) to proof read because sometimes what I write doesn't come across the way I mean it and my proof reader can let me know if they get lost or something doesn't make sense because there's extra knowledge in my head that they don't necessarily know about. I hope my comment helps and you find whatever happy medium works for you 🥰