it's a shoujo manga

i don't remember much, but it's about a girl go to this delinquent school.
she just a normal girl, but for some reason she become the leader of the school delinquent by accident.
because she smack the (before) leader by her school bag, and in her bag has a metal.
the rule is if you want to be the (next) leader, you have to beat the (now) leader.
so, she always been chasing by dangerous people who wants to be the leader....

it's a comedy and romance manga
but forgot the name...

I'm pretty sure it's Aa Itoshi no Banchou-sama.

YES, IT IS!!
Thank you so much 😀