You should delete this GA then and create a new one.

You need to delete the GA then so you don't get suspended.

Ask for the permission from the winner to delete the giveaway or change the giveaway game to the correct game, then create a support ticket.

You don't have to cancel it, just buy me the game, that will do.

I made a similar mistake a while ago. When the winner came to me, I just bought him the exact game, no excuses or bullshit, because I knew it's on me, and I am a man of my word. I was in debt, by the way. "I can not because I do not have 32€ for the game", try harder and come up with a more plausible excuse.
The giveaway title should reflect the actual content, not something else, or excuses will come up and frustrating giveaways will be rampant. There's a time window where you can delete it before the giveaway takes effect, but you missed it already.
No more craps from now on, looks like I have to mark it "Not Received", meanwhile, I'll let the administrator know what is going on.