The Bounce ability that you can unlock at Oxbury Island can be a little tricky to master when you first unlock it. It will allow you to bounce on the various bouncy surfaces throughout the game, but you'll need to have specific timing in order to keep up the bouncing.
We recommend trying to aim and hit the jump button when Stella is about halfway down her fall after bouncing. This should give enough timing for the bounce to register and allow Stella to fly higher.
The bounce ability being a little frustrating to learn is normal. Keep trying, and eventually you'll be bouncing and soaring with the best of them!