Facebook Marketplace Scam?

I listed a textbook on marketplace the other day and immediately got an offer. Rodri Peterson wanted to pay me $90 for a $40 book. Fishy right? Well, I fell for it and told him to send the money. But as I read some articles it is definitely a scam. The check arrived at my house today. What do i do? Open it and report it? Return to sender? Cash it? HELP!