Some years back I had a similar conversation with a very close friend of mine. Actually, the topic of our discussion was cannabis. We had been discussing our faith in God and the impact it had on each of our lives when the question of smoking weed came up. This was his take on the subject, which I think is applicable here.
He said there are always going to be those people who are going to try to shame you into behaving the way they want you to. They will tell you that this is a sin, or that is a sin. They will tell you so many things are sins. Any behavior that they don't approve of, they will tell you is a sin. But you can search your bible from front to back and you won't find a lot these so called sins. In your heart, you know right from wrong. That is where sin lies. Sin is in your heart.
If in your heart, you don't think smoking weed is a sin, then you might smoke a joint, find your mind elevated, open your bible and see deeper meaning in the scripture and find yourself feeling closer to God. But if you believe in your heart that smoking weed is a sin, but smoke it anyway, the you are sinning in your heart. The same goes for playing poker. Not the feeling closer to God part. I'm pretty sure you're not going to find anything about gambling in the bible. But if you do it in moderation, and don't cause your family to suffer from it, and perhaps put a portion of the profits to doing good deeds, then I don't see it as being a sin. But if you feel in your heart that playing poker is a sin, but do it anyway, then you are sinning in your heart.
Bottom line, it's not for me to tell you whether or not it's a sin. You have to search your own heart and answer that question for yourself.