The title says it all.
Don’t worry about what others will think. Don’t worry about whether it’s good enough for publication. The story is in your head, maybe the whole thing, maybe a scene, maybe just a single line, but it’s there. And it won’t let go.
So write – sit down and write. Write for you, because you’re a writer, and writers write. It’s what we do.
Start at the beginning and keep writing till the story’s done.
Later you can polish, tweak, fix. That’s later. For now, just write.
What are you waiting for? Write!