I'm a believer. I pray that I might win in lottery,sweepstakes, casino...I won....is this a sin?

If one is a believer, then they have to believe God is governing their lives and that God will provide things needful to their highest spiritual good.

If we waste time going to casinos or waste money buying lottery tickets---are we putting ourselves under God's care or saying what God has provided is not good enough and we want to do things our way. 

Is it a sin? It is probably more of a deception. It is worldly thinking and a desire for the worldly things we gave up when we came to Christ.