Ok I tried it again and it works like you said.
I suppose the initial confusion stems from the fact that the game is lacking "juice" right now. In other words, it lacks feedback to the player's actions. In my first play I would shoot one asteroid and the bullet just simply vanish without anything else so I assume nothing happened and then I tried shooting a different asteroid, same result, not knowing that the asteroids are supposed to have an amount of HP and you have to repeatedly shoot it a few times. In a complete game they would do things like flashing, showing a number of damage dealt or play a sound when you hit something etc..
On the tutorial side, I did figure out for myself the controls. You should still just write it out in the description anyway though, you should never assume other players knowing anything about your project. You can update the game page right now even during the jam.
This is all to say that it's ok, it's a jam game and nobody expects a perfect game. It's just feedback that you can take for future development of this project or things to be more mindful of for other projects.