Affiliate Marketing Secrets

I cashed a (SCAM) check from Global Test Market, consisting of 3,990 in exchange for “secret shopper” benefits. It was a cashier check. I cashed it at Sovereign bank. When I called, the bank told me no one was available in the fraud department to help me. I really don’t want to get into trouble for not knowing what I was doing. Is there any way to fix this? Please help. I don’t know what else to do and don’t want to be fined, or even sued.