Help...Scam!!!

I just found that I have been part of an online scam. I had applied to be a mystery shopper and today to my surprise was told that it was all a scam. Is there anyone that this has happened to that can offer me any advice? Yes, I did receive checks and cashed them at my bank. I don't have any money already as it is...how will I ever pay this back?

Update: Sadie thank you so much for your comments! I agree with the bank protecting me. I've been a member (and it's a credit union) for over 15 years. This is the first time anything such as this has ever happened. I was told that I would have to pay all of the money back. What about the bank having insurance and protecting me? It's so interesting to me, that I can deposit a check in my bank via telephone, but they don't have the technology within the bank to immediately identify a fraudulent check?? I'm so confused!