I don't see any source in your GitHub, just a gitignore and license file. Your source is everything someone needs to download your game, open it in the game engine, and hit Play to play the game. Here is an example of the files to include: https://github.com/icepol/DeathIsOnlyTheBeginning
If you are new to GitHub, you don't have to use it. You can delete the Library folder in your project (it has to be regenerated on each user's computer anyway, so it's not needed) and then zip your project and upload it to itch.