You have to activate won giveaways or you will get ban.

From FAQ:
Can I enter a giveaway for a friend?

You should only enter to win giveaways for yourself, and if you win a game, it must be activated and redeemed to the Steam account used during registration. If a friend is interesting in joining giveaways, they'll need to register for their own account.

http://www.steamgifts.com/about/faq

Why did you enter this giveaway then? You should have informed the person who ran that one to request a reroll... Most people want to give games away to someone who wants to play them. Unless the giveaway is from a different source. Then that's cool I guess.