TL;DR:
Support has been contacted. A new winner will presumably be chosen as soon as my ticket reaches the top of the list...

Congratulations for winning a giveaway you had a 0.153% chance of winning (a 1 in 652 chance)!

Congratulations also for your honesty! At your request (thanks! Honesty is always the best policy!), I've requested another winner from Support.

When Support approves my request, the remaining entrants will have a tiny bit larger chance of winning. ...unless more of those awesome entrants have obtained copies of WASTED, as well, in which case it might be better just to create a new giveaway (unless SG factors in the current Steam Library of each entrant, in which case the chances might be larger than 1 in 651).

(This is the first time I've had to request a new winner. When I do so in the future, it will never again be the first!)

Edit: Giveaway rerolled and new winner supplied. Key sent.

Hey Narmotur, are you certain you didn't try to activate the key in place of the one you'd already won? The reroll gave me a new winner and he says (as you can see below) the key is a dupe.

Did you somehow end up with an extra WASTED key if you won it twice as you indicated?

Please come clean on this; doing so will only help you in the collective eyes of the steamgifts community.

Oh no! :( That's not good! I never redeemed that key, so it must have been taken, inadvertently or otherwise, by Narmotur, the first winner. Which means that—only if that's what happened—he's got an extra key for you.

Steam was giving me a lot of trouble earlier today. steamstat.us seems to be acting correctly now. Viewing the stats for the past day or two at https://steamdb.info/graph/ shows some pretty big breaks in Steam's availability, but whether that's on steamdb.info's end I don't know.

Earlier, Steam was downloading updates but telling me I wasn't logged in and that I must log in to access things when I was logged in, etc. Something I haven't seen in... a long time, if ever. During the typical Tuesday afternoon/evening updates, the client typically says OFFLINE for the duration, but that wasn't the case 12 hours ago.

I'll double-check the actual key vs. the one I sent you, as well as the steam client's own stats...

Key checked: It's the same key. The only other person who had that key was the first winner.
The graph at store.steampowered.com/stats shows the outage, but it looks like less of an impact than what it felt like, and the two-day graph will have moved beyond the 'outage' before long.

I don't know what to say except that I'm very sorry it didn't work out. I hope that key will work successfully for you once the Steam content management servers calm down (if it's still an unused key). I don't think I'll try to activate the key myself, because if it works I'll have a game I don't want and I won't be able to give it away anymore.

I have the feeling that the reroll was unnecessary because the key was already taken. I'm glad to have made new friends as a result, and I hope to turn this unpleasant situation into a positive one by demonstrating in the future that I've learned a lesson here. It means that it might take an hour or two more for me send winners their keys, but if it will help to reduce the number of users either intentionally or accidentally abusing steamgifts and hurting the reputations of honest users in the process, it will be worthwhile.

Thank you both for your generosity and patience. All worked out for the best in this, and I hope I never lost faith in either one of you at any point. :) Either way, now that we've all three been involved and sorted this issue, my faith in the basic friendly nature of humanity has been bolstered.

I'm reminded of a milking stool, which is stable even on uneven ground because it has three legs!