:O OH MY GOD! You've come to the right person to ***** about this - I can't f***ing STAND P.E. teachers, they're always so harsh. They have this power-trip thing going where they want to feel like drill sergeants in the army. I wouldn't worry about it, and the thing they never tell you at school is that PE doesn't matter for one f***ing thing, it's a filler subject that they try to make legitimate with the excuse "oh kids need physical activity".
But this woman sounds like a harsh little *****, and you should explain that to your parents. I'd personally wear that D with pride. PRIDE, my friend.