<p>If your essay “borrows heavily,” in your words, from another source, you have to cite that source. Because you didn’t cite that source, especially being in a classroom situation, I’m afraid to say I think your teacher might be right. 
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<p>However, I think if you talk to your teacher you two might be able to work something out.</p>
<p>Edit: I think that freedom of speech has little to do with this.</p>