Scared about my last middle school [7th grd.] track meet!!!!!! URGENT MEET

IS 2MARROW!? any help? tips? warm ups? im running the 8 hundred because every time i run the mile i hurt my lower part of my leg[betwwen knee to heel.] [on right leg.] soooo i really need to do good today......... yeah..... so any help please URGENT MEET IS 2MARROW!
please help!!
Lauren~~~