the enemy must've spawned behind you and you decided to leave. Try turning instead of moving forward.
Ya, the controls are clunky.
You are right. The people I play tested with the game (after the jam), had to play it 4-5 times before they developed a technique and actually stood a chance at the boss (4th wave). As for the accessibility of the controls, only the up and down makes sense. 1234 (+space) doesn't. And turning the wheel doesn't convey the correct information.