Plan it out in an organizer like the one attached. Start with the thesis, add as many supporting (or disproving) claims as you need paragraphs. Then add as many details as you can but 3 should be enough seeing as you only have three hours. You'll have to com up with a good intro but use this rule for your conclusion.
How to write a Conclusion
1) Look to the future- what lies in the future of this topic
2) Touch Back- restate some key points
3) Heart of the Matter- relate it to something your reader can relate to
4) Zinger- leave your readers thinking about your topic
Keep in mind that does not work for all conclusions. Sorry for boring you with this paragraph, but I hope this helps. Let me know if you have questions.