I think its broken... the Dimond just kinda spawns wherever it wants, and each time you click AND release it registers so you just loose after like the second round
Viewing post in Arc's BJ Training [Demo] comments
It works as intended for me while testing, which platform are you playing on? You're not supposed to click as fast as you can, which is how you lose points. The goal is to build momentum, as stated in the tutorial. I suggest trying again and seeing if you can get past the second round after some practice. Aim for the stars and use your Burst meter when it fills all the way up.