What should I say to apologize to her?

So, in the beginning of the year, I met a girl named Sam. Me and her instantly become best-friends, like sisters. We could relate so much. It's like we were living the same lives. Every day we hung out, and always texted each other 24/7. Then one day, I decided to make a dumbass decision. We skipped lunch like we normally did, but this time, I had the idea to go to a classroom and steal peoples iPods, iPads, money etc. Basically, anything valuable. She didn't agree at first, then I pressured her into it. But she didn't steal anything, she was my lookout to make sure nobody was coming. When I took all the sh*t we were like ''Okay, lets get out of here!'' and we put our bags back in our classrooms and skipped the rest of lunch. Latter on in my 6th period, I got called down to the office, thinking ''Oh, it couldn't be that!'' because I was always causing problems, so it could've been something else that I did. But, I was wrong. The principal said people were reporting their stuff missing, and the reports were made at the time we had second hour lunch and he noticed we weren't there, and we're always skipping and usually got caught. So he started asking questions where we were, I denied everything and lied. Then our school cop walked in with her, and she told the truth. She didn't know I lied, she didn't know that he had asked me questions already. So they went though my bag, and took all the sh*t back. So I got suspended for four weeks (one month), which included time for me lying. If I didn't lie, I probably would've only got two weeks, or three, I don't f*cking know. She only got suspended for five days since she didn't steal anything. And her parents are really, really strict. They don't want her f*cking around in school and not caring, they want her to do good and pass and go to college. But since I got her suspended, they hate me now. And I'm not allowed to talk to her or see her again, the school even said it, like wtf? They have no say in that. But, since I got her in all that trouble, she hates me now (I think), and we haven't spoke in months. We had all these summer plans, now their all gone, and so is she. I really miss her so much. Also, a few people said she talked about me in school (in a good way) ever since we stopped being friends, and I always saw her looking at me whenever I was around her. So, should I add her on FaceBook and send her a message trying to apologize? I want to so bad, I miss her. I just don't know how to do it, what do I say? And if I end up messaging her, which is what I'm asking help for is what to say to her, I'm gonna tell her I'm not gonna be a trouble maker anymore and do those stupid things. That is something she didn't like in our friendship, I can tell, even though she never said anything.