Falsely and unfairly accused of plagiarism?

I recently wrote a paper for my college lit cl, asking what is the american dream and how does it relate to the Great Gatsby. What an original paper idea.........anyways, I wasn't even sure how I wanted to define the American Dream, I havent spent time on this subject. So i did a little googling and after some research with just some blog-ish type sites and random places, I formulated my definition of the American Dream. Since this is a definition, turns out some website has a definition of it similiar to mine. They call it the "driving force" in the book, and in my opening of my paper, I call the American Dream the "driving force" as well. Now let me tell you this is 2 short little sentences in my opening paragraph, and I received an email without warning letting me know that i committed "academic fraud" and it was already reported to the boss of my TA. I have NEVER been accused of such a thing in my 13 years of schooling, and my writing skills is something I pride myself on and I plan to be a journalism major because I love to write. For my teacher to think I purposely was cheating my way out of developing a paper hurts me and I am deeply distraught by the accusation. I am in the Honor's program here and am on the Dean's list with a direct admission to the journalism school....why in God's name would I be the kind of student to cheat? I don't skip cl, and I'm always on time and do my work with integrity. Does anyone have any hints on how to handle this tricky situation? I stand by my paper and I fully developed it in my own words and thoughts, and I do not believe this is a case of plagiarism what so ever, and I don't know how to win this war!