I'm so sad and angry after what my English teacher did to me..

I'm French btw and we study English at high school. So we did a test where we had to write an essay about an experience that changed my life.
And today when he gave us back our papers, he told me that it is too sophisticated and good to be written by a high school student.
And he gave me 3/20, and it's a very important module :(
I'm so sad because I did something great and instead of being praised, I'm being yelled at...