Hi, when you press space or left mouse click, a down force is applied to the ball, also a small force to the right is constantly applied to it as well regardless. You have to press down when the ball is about to go down a slope. If you get stuck in the middle of a wave, don't keep pressing down, do little presses so the ball has time to oscillate. If you keep pressing it will just get stuck in the middle.
If you still have problems with it don't hesitate to ask! Hope you get it to work <3333