Except for the part about how people you least expect will remember you and look up to you as role models and how they are more educated than the majority of the world, I don't think you are telling them anything they haven't heard before: "you are the leaders of tomorrow, do your best, blah blah blah." Cut all that crap out. If you're going the route of a "real" speech, keep it insightful. For example, did you actually talk to any of the people who recognized you? What did they say? Why did they remember you? Or did they just say "hi?" If that's all that happened, then it's not a meaningful story and you should look for a different example. It might be better, say, to tell how you were influenced by your friends, who in that case would be role models (most people, especially in high school, don't recognize their friends as role models).
Or if you can't think of anything like that to say, and still want to give a "real" speech, then just talk politics or freedom or something. Tell them how a little bit of piracy is good for society, or rant about frivolous lawsuits, or something.
Or go funny.
