Theres a few things to keep in mind when uploading to WebGL.
1. make sure the .html file isnt the name of the game but "index.html" without quotes
2.make sure none of the exported files names doesnt have spaces
ie. my game.js should be either "mygame.js" or "my_game.js"
3.Also make sure you dont have period sign( . ) in the name.
my.game.js should be mygame.js
I was calling my game "Dr. Rewind". itch.io hated that I had it so i change the name to "doctorrewind"
4. keep the file names lower-cased to be safe
Heres my game if you want to check it out: https://chevon.itch.io/doctor-rewind