I'm not sure what you mean when you say the money "is still on the game." If the money is accessible to you, and you could easily take it at any time, then you have what is called "constructive receipt" of the money. The money is yours and you have to report it as income and pay tax on it, even though you haven't actually taken it. It's the same as if you had the money in a bank account and could withdraw it at any time. It's your money, even though you haven't taken it out of the bank.
To decline or refuse the prize, you would have to take some action to have it removed from the game, so that it is no longer available to you.
