Your teacher is right, I used LOST as a text for my prelimnary speech.
You have to be concerned with a few important things:
-episode choice (try to pick something that will give you lots to talk about in techniques and evidence of imaginary journeys e.g episode: white rabbit season. 1)
-Don't recall the story of the episode, I had early problems with that when writing my speech. So re-read what you've written and ask yourself does this answer/link back to the question.
-have a recording of the episode so you can re-watch the damn thing over and over and over. That way you can pick up anything important or important quotes. Not sure if there is any online transcripts of episodes.
I'm sure your teacher mentioned this but make ure you have a variety of text types to talk about.
Good luck with that!