Replying to How to break bad grades to your parents? help please

ok, i tryed searchbaring this but it was hard.

so i have gotten straight A's all my life. one time i got a B+ and that got my mom worried enough to call the teacher and make sure i was doing ok wiht everything. my mom is one of the biggest tightasses ever. and she's a complete bitch. i don't really have time to go into detail on her but just trust me. now here's the thing i need advice please. grades are about to come out and i'm pretty sure i'm gonna get at least one, maybe two bad ones. like Cs or worse. how do i make it seem less bad? she like wants me to go to an ivy league school or something so i think she's gonna kill me. and the worst part is, i'm afraid she will make me quit baseball, my second favorite sport to skiing, because all this is happening during my first season on the high school baseball team. any help/advice would be GREATLY APPRECIATED. thanks. oh and sorry i didn't clean it up, i didn't realize it was that long.