You had better get on it ASAP, as soon as the bank is open. The check is fake. You could be in some serious legal ramifications for depositing a fake check!!! Not to mention financial problems as well. Please, please do not delay.
There is a real company named Arden Services. Scammers use the names of real companies all the time to perpetuate this fraud. It's been an ongoing issue for years, and many, many people have fallen for it and been out a lot of money and then not been able to have checking accounts at any banks.
Real mystery shopping companies pay about $15 per shop and you get paid AFTER you do the work. It usually takes a month or more to get paid. There is a link (Official List of Mystery Shopping Companies) at the bottom of this page with legitimate companies that you can sign up with.