What did I tell you? Yes, grammar matters. Just because she gave you a bad grade doesn't mean she's anti-gun either. You might not have provided much of an argument, only your opinion. If your paper is any indication of your writing skills, I'm not surprised.

Do you use your schools writing lab to proof it? Let someone else read it next time.

Don't say I didn't tell you so. The purpose of the assignment is to provide and cite a side to an argument and be convincing. You made the assignment even harder because of your beliefs about gun control. Not that your beliefs are wrong, but it's hard to remove emotion from equation when you need concrete and cited facts.

Best thing you can do is come off your little high horse and talk to her about what to do to make it right the next time. You're learning, remember?