Yes, it tells me it's a duplicate

Just saw your post, make sure to hit reply right below my comment so it replies to my post and I get notified with a message.
As for the random key you provided, I'm going to pass(not using it) and do this by the steamgifts rules. You can either obtain a copy of GTR Evolution Expansion Pack to give away (check steam store or the trade section on this site) or simply not provide the game.

Duplicate keys aren't totally uncommon, and since this sort of thing happens I don't think you'd be suspended or such for not delivering the game. You'll just have a giveaway that's marked not received, which isn't a huge deal unless it happens regularly. Sorry this happened, as I would have liked this expansion :/