Hey,
I really like the actual game play idea. It's pretty similar to Pontypants submission to Brackey's gamejam but I don't mind. I am not sure how well the "one life" theme fits to the game play idea. I think the controllers are bit harder than Pontypants due to the sphere collision which makes it harder to balance two or several balls on top of each other. Balls needs to be exactly on the middle so the top ball does not drop off. Pontypants game colliders are rectangular which makes better use of the whole top collision width which can add interesting addition to the game play, in my opinion. (look for Pontypant's submission to Brackey's game jam from the YouTube)
Anyway, this is one of the better working games without any bugs per ce and actual levels for a bit longer experience.
Good job all in all! Keep up the good work!