Actually, same here! I used to get overwhelmed by just the thoughts of contributing to GitHub projects too, because I think my code was kinda bad and I didn't want to get judged at. Whenever I thought about repo maintainers/reviewers, I always imagined that they would be all like Linus Torvalds, and I was afraid of getting shamed for my poor code, lol!

I was lucky because I had skills in drawing arts, so I started by contributing icons to an Android icon pack project, which didn't really require coding skills, and is actually something I know I can do. The maintainer of my first contribution turned out to be a very friendly and cool person instead of someone grumpy and direct I always had images of in my head! From there, I gradually learned about the tools and coding a project.

I think the truth is if you want to contribute, even when you think your code isn't up to standard, you really still need to start somewhere. If you don't feel any confident, start forking a small project with some incomplete milestone that you know is something you can do, I think? Just remember that not all reviewers are out there to chew on your code, lol.