Where is the Pew Pew achievement? [spoilers]

First of all, I must say that I absolutely loved this game.  This is definitely the best Nifflas game so far.  I've completed everything except the Pew Pew achievement.  In the area below Chapter 3, I finished the area where you find the baby and the area where you switch between Mi and the ball.  I'm hoping I don't need to complete the area with all the magnets, I found that unbelievably frustrating.  Can you give me a hint on what I need to do for the achievement?

Thanks in advance!

The area it's in is:

If you go past:
you have gone to far.

There is also a secret in the secret, but it's one way, away from the pew pew room, so just follow the main path.

Found it, thanks!