Bless you but it's a gift worth [at least] 100€. Just fyi.

If you are indeed dedicated to gift it please make sure the winner activates it. I think quite a lot of alt accs & resellers will enter this one.

Well, I thought it was some other version. So I should get out of the distribution?
Although. I checked on STEAMCHARTS, there are 3 versions of the game.
This version, and that were mentioned above.

You should be aware that the Duke Nukem 3D: Megaton Edition has a different app id (https://store.steampowered.com/app/225140/) than just Duke Nukem 3D (https://store.steampowered.com/app/359850/). This will get the winner in trouble if they activate the megaton edition and say they received it, since it will appear, to anyone who checks, that they didn't activate a game they won. I know it's very technically but you can/should ask support to change the give away to the correct app id if possible.