Many thanks for all the tips. I've kept the levels in the game very small and that's why I've made it so that if you lose a life you have to start the level all over again. I loved that in the old games. Yes, it was annoying at times, but that's why I included the level codes. So you have to think carefully about whether I can kill the enemy with the arrows or whether I should jump on his head. That was always a challenge and I loved it.
The two buttons, one for jumping and one for shooting, should actually work