[US]fake checks scam/ money mule scam or am i being paranoid

i run ads on yelp for a construction jobs on the side, i got a message from someone saying what they needed done and a full scope of everything and seemed pretty legit, they sent me a check for 15,000 through ups and said it was for materials and some other things they bought for the house they have(i am working on) they tell me to send such and such amount to a supplier and i’ve already deposited the check but haven’t sent any money, im starting to realize how stupid i am, is this a scam or am i just being paranoid?also what should i do if this is a scam?