I am a student, and I can completely empathize with how you feel. I can tell you that a lot of what I've seen is that it's one-hundred percent completely worth the stress and fear of rejection if even one long-shot (in your mind) pays off. I've had that happen to me firsthand, and I've seen it in other people. The more experience you have dealing with tough problems, the better you'll be thinking about them, and tough interview problems by extension. Just make your interview count as best you can, and step back and wait. I promise it's worth it.