Some other tips for this one that helped me out.
Firstly, when playing the game - have a gun with a small aiming laser (contact/plasma are good, but most should work).
Secondly, getting the ball into the "hoop" without hitting any of the sides of the "hoop" will award two points, instead of one, for a non-multiplier shot.
Use the small aiming lazer of your chosen gun and aim for the middle of the hoop, should make it easy work, even at stage 6.
All the best ^^