Shoplifting charges, what to do?

Long story short, a "friend" of mine (no longer!) was stealing from stores and I didn't know it.. she had me hold the purse because we had to go back through a store she stole from to go to the car and since I didn't know (she said her shoulder hurt) I said okay. Well it seems the reason she did is they 'saw the merchandise go in the bag' and the security made me come to an office in that store(her a separate one). I said over and over it was her and asked if they can check the cameras top see it wasn't me but they said since I had the bag it doesn't matter I'm at least an accomplice and have to take responsibility. She'd taken stuff from other stores too which they returned to the stores however they only made me sign acknowledgement for 2 things which added up to $75 from the store SHE (to them, I) got caught in. I assume that's all I'll be charged for? They said I had to go to court and that I could fight it and say it's her but since I don't have proof they said I should just own up to it and if I have a clean record I would probably be okay.. jerks. They said it looks bad on me because I'm 18 and an adult and she's 16 a minor. I'm in the state of Maryland.. what should I do?