Originally, I Was A Delinquent, But Now I'm A Serious Girl! シュレーディンガーの猫

I was a former delinquent, but when I entered high school I got serious.
My grades aren’t good, but my behaviour is adequate. I have 0 friends because of my face and a rumour.
One day, I received a nutritional supplement drink from my younger sister, so I drank it at school.
Then, my body changed, my chest swelled up, and my butt became big. My waist became thinner, my shoulder breadth got narrower and my hair grew. Also my height shrank?
This looks like a girl… does it not?
How did this happen…
Is this seriously a story about a stupid girl?