I won the game I already have and revealed the key

Thanks, I hope I won't be suspended

I bought it from another source, can't refund.

No. You cannot create a giveaway with a key you've won on a giveaway here.

Even if you could you shouldn't. If you already own a game you win the proper way is like thoughtfulhippo said. Inform the creator and ask for a re-roll preferentially before viewing the key.

You can get suspended for doing something like that on SG. You need to take a few minutes to read the FAQ and Guidelines.

happy cake day

happy cakeday!

You can check that for yourself: "An icon with an eye will appear next to the key once it has been viewed by the winner."

It's hard though sometimes if the winner has 3k+ games in their library. Compare2steam no longer works so you have to just wait for Steam to stop breaking. Do you have any tips for a better website to use?

Yeah, but this time it wouldn't work. I was dumb enough to buy game AFTER I won it here... I just needed to click the tab in browser, but instead I bought the game and did it outside steam, so I can't return. Best deal ever.

From FAQ:

What should I do if I win a game more than once, or if I win a game that I already purchased?
When this occurs, you should contact the giveaway creator and inform them you will not be accepting or redeeming the gift. Explain the situation, and ask the giveaway creator to request a new giveaway winner. During this process you should not mark the gift as "Received", or reveal the key if the option is available. This will help inform us that you are not accepting the gift, and it will prevent you from being suspended for not activating a gift you won. Once the ticket from the giveaway creator is approved for a new winner, the win will be removed from your profile.
When should I mark a gift I won as "Received" or "Not Received"?
You should only mark a gift as "Received" when you have both (i) received the exact game described in the giveaway, and (ii) activated that game on the Steam account you used during registration. In all other instances you should mark the gift as "Not Received" one week after the giveaway has ended.

You should write in the giveaway and wait for response. If you don't get any response you can mark as not received after 7 days but I would just leave the feedback open. It doesn't harm you. Also you won't get suspended as long as you post and explain the situation in the giveaway. AFAIK mods check the giveaway and/or tickets before taking action.

You won't get suspended for not activating the DLC for the same reason that you were able to enter in the first place - SG doesn't see if you have a given DLC or not. Also for that reason, you should always double-check before entering a DLC giveaway.