Won same game twice, what to do?

Tell the person giving away the game to request a reroll. I presume you won two at the same time?

Also I suggest you have a strong look at this.

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

Post on that giveaway page requesting a reroll because you won it twice. Mark as not received after 7 days.

happened to me, requested reroll on giveaway page - problem solved shortly after

Request the reroll by making a comment on the giveaway page and don't do anything with the key (no regifting, trading, etc) and then contact support to cover all bases.

Ok thanks gys :)