Cool little game!
I feel like the concept of a reverse peggle is one of the few game ideas that hasn't been used too much within this jam.
The first levels in which you can place as many pegs as you want made it feel like I was playing a different version of sugar sugar, but I'm glad that the gameplay got more varied afterwards. But I think the later level with the pegs as targets solves this issue.
I liked placing the lines, since they were more limited in the amount I could use so I had to think a lot more about where I got to place them. It felt like I was in more control of where the balls were going to go overall, instead of being able to control the direction of a single ball once.
The last level was definitely the best, and I think that this is just because of the predictability of the shots. You can actually make the ball go where you want it to. In the previous levels, half of the targets I got seemed to just be be chance, and I wasn't able to effectively redirect them how I wanted to. I think you should have more consistency on where the balls will go, so the player can more effectively bounce them around.
If you wanted to keep the randomness of the shots, since we technically aren't supposed to be controlling that, you could also have some sort of slowdown mode. So we can place the pegs in time to where the balls were shot.
The piano effect was a cool idea, but I think it got a bit overwhelming when there were a lot of balls on the screen. It really sounded the best when there was only 1 ball on the screen.
Nice work!