Shannon, please turn the check over to your postmaster (it's mail fraud) or contact the FTC (Federal Trade Commission). As MFJ posted, it's a scam. The money order is fake. Often the scammers can produce sophisticated money orders/checks that your bank will not initially detect as fake, but after you deposit it, up to 10 days later the bank will discover it fraudulent and you will be in trouble both legally and financially.
This site is a place for mystery shoppers to congregate and discuss common shops (restaurant shops and some retail shops). There are 100s of shopping companies out there (there is a list below). Like MFJ stated, you get paid weeks later after completing shops, and not large amounts most of the time. Usually shops pay $15-$40 per assignment.