Is it illegal to submit a story in a major examination that contains an excerpt from a published book?

I'm 16, a Brit and taking my GCSE English examination in about a month. I've written a story which I believe would score me high grades, but it contains an excerpt from the book 'American Psycho'. The paragraph i used contains roughly 50 words and has been sparingly edited. My question is, like my question stated, whether i would be penalized for copyright issues. Like, will my script be disqualified because of this? Help greatly appreciated! =D