For a three hours jam is great! I would add more juice like: particle trail from ships and shooting, explosion particles, camera shake on deads and asteroid explosion… I would also make the gold more attractive (glow, tweens or animations) Also, I like the idea of getting gold from asteroids because while you shoot you are in bigger risk so that fits the limitation imho. In fact I used a similar approach of risk/reward.
I had to get an old laptop with windows to play this game haha. I suggest that you build also a web version and you’ll get more reviews. Many devs don’t use windows.
Keep it up!