No, that's not the case. Bitcoin exchanges are provably fair by default. I mean, if I deposit $1000 to bitstamp and they only give me $500, then I know I was ripped off. Hence it's provably fair. With your site, I have no way of knowing if I got ripped off, which is what makes it not provably fair.
The advice I give to people wrt to provably fair, imagine you were an evil bastard absolutely intent on stealing peoples money. Think about how you could steal their money without them noticing (e.g. using house bots that see how much they deposited and then beating them). Now, if you could come up with a way to steal peoples money undetectably, then the game is not provably fair. If you can steal money, but they will be able to see that you stole their money, then the game is provably fair.