I work with the person who handles all academic dishonesty cases at my school, and we have talked about how people handle themselves many times. If you lie or act put off/rude/dismissive, they will not show you any mercy. The people who have had the most success (as in, had the least harsh punishment, like failing the assignment) went into their hearing and said something like, "I made a mistake and I understand why I shouldn't have done what I did. I deeply regret compromising my integrity and risking my academic career that I have worked honestly on up until this point."

There was a guy a few weeks who was supposed to graduate this quarter, and probably would have just failed the assignment he cheated on, but instead he acted like "yeah I cheated, but it really inconveniences me to get in trouble, so can I just not?" He was suspended for the semester, had to quit his on-campus job, and won't be able to graduate until December now. Everyone on the board kind of just had the attitude like, "sucks to be you, dude." He didn't acknowledge that what he did was wrong. So I would suggest speaking from the heart and expressing respectful regret. And take whatever punishment they give without making a huge scene. (It's possible that they have an appeal process as well)

Make sure to communicate with whoever organizes the hearing, they can help you and tell you your next steps. At my school, people are allowed to bring a support person with them (parent/friend/uncle/ect), and even though they aren't allowed to speak for the accused, they can confer together and help privately.

Basically, if this is your first infraction, you probably won't get expelled. Good luck!