How do i look more "aggressive" when i pitch?

My highschool softball coach said when i pitch i do very well but i need a little more? Like i just go up and pitch and even when i do bad i dont show if it affects me, i think she wants me to show more confidence and aggression? I dont know how to do that because im just a quiet shy nice girl hAha so its hard for me, any ideas pleasssseee?