Here's video of me playing your game with some commentary:

https://mega.nz/file/6JFC3YCC#Z-VAEMRyF6JZ48Eod1x6Fq-o2XiP7ic4zvHIIB-V5j0

I hope it's useful.

Neat! 

Played through it and only ran into a couple of weird issues, nothing gamebreaking tho

Ball hit the corner and lost all it's speed and fell, leaving me staring at the top:

Also had a line lose all it's colision and become unable to be erased.

Had fun tho, took me back to my Linerider days ^_^

Good Luck with your game!

Hey there, cool little puzzle game! I think the idea works nicely. I didn't play too far in, just to level 5 I think. But I had some good moments, and felt engaged. From playing those levels though, I will say I think the levels with the boosters feel a lot more fun than the levels without. On level 5 I think it was (back and forth), there was a dip for me, because it felt like I was trying to force the ball to move along. And it kept just crapping out. I was drawing ramps at the most slightest angle so that I could try and get it to go the distance, which I don't think it too great of an experience. Seeing the ball whiz around a loop and off a ramp is there the fun is.

Also, this might be a stupid question, but why a cube instead of a sphere? A sphere somehow seems more fitting for the idea, and the corners aren't really relevant anyway. That might also have more nuance in how gravity interacts with your ball (as opposed to on/off) with the cube. Eh, just a thought. 

Nice work! Puzzle games are hard to get right imo, and you've gotten past most of the pitfalls/mistakes I see a lot of games make.