Ah, I see. Maybe it's not so clear that stages 3 and 4 are special stages where you only have one life (at the current game version d-250709_0). That's my fault I guess.I believe you just reached the stage where you could only hit the wall once. Have you tried pressing space to respawn, or enter to pause the game to be able to go back to the main menu? If you did try that and just got stuck there, then it's an unknown bug to be, and I'll keep looking into it.