Right...first, find and watch a show called Re:Creators. It deals with a lot of this stuff, and it WILL help. You can find it on Amazon Prime and on other, less legitimate anime websites that I will not mention here. But, legitimately or not, watch it. Characters say stuff in it that I think you need to hear.
So, I am the author of Diablo:Demonsbane, the e-book that launched the entire Blizzard Entertainment fiction line back in 2000. I would have been the author of a few more fantasy novels if those pesky publishers hadn't glutted themselves on manuscripts after the Jackson Lord of the Rings films. I've written several non-fiction books, I was one of the first online video games issues columnists in the English language, I've recently collaborated with Ed Greenwood (creator of the Forgotten Realms) on The Eternity Quartet, and I own my own publishing company. I stopped counting my article publication credits after it hit number 250. So, I may not have become the next Stephen King, but almost 25 years into my career, I think I've held my own.
I finished my first novel when I was still in high school. It was called Demon's Vengeance. 65,000 words. And it was terrible.
It was so bad, in fact, that a few years after I finished it (after I'd polished my style writing Highlander and Doctor Who fanfic for a while), I actually wrote a letter of apology to the editor at Tor I had sent it to who had asked to see a copy of it when I mentioned it on a newsgroup. I felt that bad wasting the man's time with it. That's how awful it was.
(Let me put it this way - the titular Demon in the book revitalizes his life force by hypnotizing and then having sex with beautiful women, draining them into a dead husk, and the problem of gathering an army for the final battle is solved by just opening up magic portals on a giant plateau. There's a test of courage in which a burly highlander swings an axe around and stops it just before splitting somebody's head open to see if they're afraid. The writing style was full of unnecessary sentence fragments that did not connect at all to the characters or situation. It was THAT kind of bad.)
Was it a waste? Hell no. The mere act of finishing it taught me so much about the process of writing that I would call the time invaluable. And even more, I knew that I was capable of finishing a novel, which is no small thing when you consider that any long writing project is a marathon. Demon's Vengeance never got shown to the public, but a lot of what I wrote afterword did. And, within 5 years of finishing Demon's Vengeance, I was agented and signing a contract with Pocket Books for Demonsbane. I even got to receive some brief mentorship from my favourite author, Dennis L. McKiernan (whose books were literally what inspired me to pick up my pen and write).
None of us start off good - the best we get to ask for is that we start off good enough. I can tell from the style of what you've written in this post that you're already there, so there's that problem sorted. All that's next is putting your story on the page.
You are going to make mistakes. Every author does that. The way we get better is through sheer practice. I'm as good as I am now because I've been doing this for around 30 years, if you count the amateur work before my first professional sale.
But, there's something else, and I don't think somebody who doesn't have a couple of decades under their belt can tell you what I'm about to: right now, in these starting years, you are going to be writing the rawest, most vital prose of your entire career. You will take risks that will propel your stories far beyond the sum of their parts. All of it will lay the groundwork for the refined and experienced writer you will one day become many years from now, but in the process of becoming that version of you, you will lose the ability to write the stories you can right now, at this moment. You will become a better writer, but also a more conservative one. Nothing you write in the here and now is a waste...and I speak from experience.