I'm firing lasers but not hitting the asteroids successfully.

Make sure you're locking onto the asteroid:

Aim your head toward the asteroid you want to target. Confirm that three yellow triangles surround it. When locked on, your laser will hit the intended asteroid.

Give yourself time to adjust to VR controls:

If you're new to VR, continue playing for a while to get used to the controls. You can also temporarily turn off dichoptic mode while you adjust to the VR environment.