Stage 3 appears to be bugged. No matter what I do, including nothing, it spams "FUCK" over and over and I get 0 points.
It's a little tricky tbh, you wanna keep a steady speed for shaking, not too slow and not too fast...
It's also momentum based, so what you could try to do is do the same back and forth motion over and over, to try out which speeds/distances across the screen work out for you, even if it shows "FUCK" at first since the average speeds takes a second to adjust itself.
As soon as you're getting the average close you should see "Bravissimos".
Good luck!