I defended my honors thesis last year and I remember I was very nervous, too. Just keep reminding yourself that you have worked hard for this, that you are prepared, and that you'll be fine.
Don't freak out when your committee members start asking you weird questions. And, don't worry if you feel like they are trying to detroy your argument... They are supposed to act like that and question everything. Just remind yourself that it does NOT mean you did a poor job, etc. They simply want to force you to explain everything to make sure you understand it.
Try to go to the room early and set up your stuff well in advance. That way, if something isn't working, you'll have plenty of time to fix it. I remember my projector wasn't working!
Wear something nice, smile, and be (at least "look") confident. Best of luck!
🙂