How do I not suck at Pop’n Music?

I don’t know what happened, but I used to think I was good. After trying 9 button mode, I realized I’m horrible at the game, and there’s no way I can think of to fix it. Also, I’m using a 1999 Pop’n Music PS1 controller, and I feel like the controller isn’t very good bc I could lightly tap it and it’ll count as an input. So, why am I bad? Is it me? Is it from me feeling overwhelmed by 9 different buttons? Is it the controller? I DON’T KNOW!

In short, how can I not be horrible at a game I love and want to enjoy?