Guys and women help! Asap?

(btw i am 11 and so r the boys)One in school i was bending over cleanin a tabel and a guy was standin next to me and then his friend came behinde me and like act like has humping me but he wasent touchin me so i dident no and then all if a sudden he hit my butt so hard and loud and i was like y did u that and both of the both of the boyz just laught and waled away. What should i di