HELP, Heros!!Do I need to leave US for H1 extension ???

I was reading all of the old messages here and found this one" I-485 pending中, 能否申請 3_yesr H1B extension? " Xiaobaitu said that he needs to leave US to appy for new H1B. cRY!!! I am in the same situation. I applied I485 during August, now my school is applying 3- year H1 B extension, but they didn't tell me at all to go out and my H1 B will expire next april. Please tell me what to do and what should I prepare?Thanks