This really hurts! :( please read! and someone please tell me whats rong/going on!!.?

okay so today during p.e after wards ( end of school) ,well me and this girl ,were like friends/frenimies (at times)..it depends, so in the locker room it was just me and ehr still getting changed and sometimes we like fight, but ina jokinly way or play fighting.. but today, i dotn really remember how it happened but all of a sudden we started to fight (we were talking about it or something like it i guess) so then we just start like Phiscialy fighting! (punching, slapping, and hitting..) and she says im not playing anymore. (in a serious voice and face).. but then all of a sudden she comes out with a kick and kicks me! right above my chest.. a little below my neck. (so hit was a high kick..) at first i felt this small pain, then it went away and i started hitting her even harder because she did that. so then after all of this was over, 1st she like threatened me and said Yeah You Better Be Scared!! in a real like threating voice.. (shes can get reallyy ghetto at times also btw) and 2nd. were she kicked me it started hurting all over again, and alot more! this all happened in the locker room.. and nobody herd/saw because they weren't around. so my parent came to pick me up after school and when i was in the car, were she kicked me it started to hurt really bad then! to the point that i was crying. (silently, because i didnt want my parent to hear and i didnt want to tell them what was going on) but when ever i moved it hurt alittle or if breathed heavily or sat up it started to hurt even more. so i tried not to move as much in the car because i didnt want the pain,. so this happened around 3 and not its like almost 6:30 and its still hurting. i just sat up quickly by accident and i felt this real sharp pain there and it hurt so much! i had to stop what i was doing and like just sit there :/ . also the girl who kicked me she used to lift weights, plays soccer and has a strong kick! plays basketball, cheers, and runs track so she has hard leg muscles!! you can even see them in her legs.! im 12 btw.. if that helps. but someone pleaseee help me and tell me what to do! is something rong there? why does it hurt so much when i move, breath heavily or sit up?? and whats that place a little below your neck? but above your chest called? i dont really know. and no havnt told my parents yet because i dont know how, and what they would say.. should i tell them what happened? if so why and how?!? please help me out ! im in pain and need answers! :'( . .thanks-