I love that you're using the Godot Engine. Big fan.
Nice effort in 72 hours for a new developer!
There's a few small things that need tweaking:
1. Godot can export to all platforms. There's no reason to have only html.
2. If you're going to export to html, you could make it playable in the browser on itch.io. Just rename the html file to index.html and make it playable on the itch page.
3. Chrome doesn't like running Godot apps locally, so you may want to advise users to try Firefox if it doesn't work for them.
4. Seems like the level fails to restart if you lose. So I had to reload the page to play a second time.
5. Consider making it auto-shoot. There's not much point clicking the button endlessly. Especially when it doesn't register clicks outside the window.
6. Try your own game on the itch.io desktop client. If it fails to install, you've got a problem worth addressing.