What should a regretful student who is caught plagiarizing do to move forward? I'm a high school student also enrolled in a computer science class at a local college, and earlier this week I noticed that my grade for the class had dropped. I checked the online gradebook after noticing this, and there was a 0 for a programming assignment I had submitted. I sent my professor several emails (instead of asking him in person because the college is currently on break) asking why there was a 0, and he responded after a few days by telling me to wait for the disciplinary committee to contact me regarding the assignment.

And only after sending my email did I remember that I had taken bits of my program from an online one written for a problem very similar to mine--and it even used techniques we never learned in class. It was months ago, when I was really overloaded with work, and I thought I was safe because I paid to access the code online. And a lot of my friends who were full-time undergraduates seemed to be overtly cheating pretty often.

And only after he responded did the full gravity of the situation sink in on me: I had plagiarized, and there was no excuse. I had used someone else's work without much remorse while I was doing it, lacking moral responsibility just like a sociopath might. I did something might ruin my life.

At this point, I'm panicking and desperately need advice. I feel terrible, and I'm finding it hard to concentrate on my work for high school or even sleep. I had an amazing opportunity to pursue something I really loved at a higher level than most people my age, and I completely blew it. And what's more, I might not have the chance to do it again now.

I was recently admitted to my dream college Early Action, and it was the only college I applied to. But now I'm afraid that I'll get rescinded because I'll probably be dismissed from the college I'm currently enrolled in, and even if the disciplinary committee doesn't let my dream college know directly, it probably has a way to find out. 

And even if I don't get rescinded, I'm worried that I'll need to send this information to all of the grad schools I apply to, or if not, they'll just have it anyway.

I know there's not much I can do until I hear back from the committee, but what should I do right now and after I hear back? If I'm brought before the committee for a hearing, what should I do? What are the chances I'll be rescinded? Will this prevent me from getting into a good grad school?
You sound quite naive about what constitutes plagiarism or academic wrongdoing at the university level (in particular the thought that paying for the code makes it okay or even less likely to be caught is pretty much exactly wrong).  But this naivete is quite well explained by the fact that you're a high school student.

It's great that you realize that you did something seriously wrong: I agree with you.  But you're not a sociopath: rather, you are a teenaged minor, and your behavior is well within the normal operating parameters of such entities.  Many (perhaps most) minors do at least one really stupid thing that if they were an adult would get them in real trouble.  But unless their actions cause irreparable harm to others, the adult world tends to be forgiving: there has to be a time in which you can make mistakes and learn from them.  

I think it is very unlikely that your actions would cause the university in which you've been early admitted to rescind its offer.  This is on the border of being so unlikely as not to really be worth worrying about...but someone in your situation is going to worry.  Here's how to allay your concerns:

You should go to your professor and explain very calmly and honestly everything that happened.  Your position should be that you are thoroughly repentant and will not contest whatever penalty to your course grade you have received.  You have just one concern: you don't want the academic dishonesty to appear on your transcript, because -- be honest -- you think that might jeopardize your collegiate career.  If it comes to it, you should make clear that you would rather get a failing grade or an unsatisfactory withdrawal from the course.  (This is a difference between your situation and that of most normally enrolled university students.)  If the professor is not willing to agree to that on the spot, then you should talk to others -- in particular, to your parents -- about how to proceed next.