Accidental shoplifting, what do I do?

Long story short; I got arrested for shoplifting $30 of stuff, It was a complete and total accident, I'm sixteen, and I've been arrested once before for going into a vacant home, I got a "Unlawful entry" charge. I am 99.9% that I have AD-HD, I pick things up all the time and don't realize I did. In this case, I thought I had put the things back, but I put them into my pocket thinking it was only my wallet and phone. I understand that this is pretty unbelievable, and I agree; but it WAS truthfully an accident, I think that the most important part of things like this, is learning a lesson, and I have; trust me. I have an drunken worthless father who's in and out of jail all the time, I have completely disowned him and cut all contact with him out of my life, just so I don't end up like him. I just got hired for a job, I plan on going to the Career Center next year for Digital Arts (The career center, is kind of like College, it gives us hands-on learning experience and college credits.) And I don't want any of this to be messed up because of a careless mistake like this. I have been trying to pay more attention to everything I do since this, and I double and sometimes triple check myself before I leave a store, I am also scheduled to be tested for AD-HD in a week. I am totally freaking out, I have a meeting with the prosecutor tomorrow to see if they will take me to court, I really don't want it to come to that. What should I say in this meeting? It truthfully was an honest mistake, and I am sooo sorry. I don't know how to handle the situation, I'll be so nervous tomorrow that they will think I'm lying. :( What can I say to prove it was a mistake, and that I really am sorry? PLEASE HELP.