I had problems with the screen size on Windows, but zooming the page did the trick.
I like that you added a little story bit to give the game some context. The snail is also very cute <3
I would suggest adding some feedback like particles and SFX to actions like picking up gold, defeating enemies, taking damage and the counter going down as you shoot, those little changes will start to add a lot of polish to your games and will also communicate important mechanics to your players.
Congrats!!