what should i do

ask the steamgifts support or add me :P

Depends on how long you waited, but wait some more then submit a ticket. you have 7 days to send the gift, meaning he has 7 days to accept it before you catact support.

As noted, you've got to give him some time. He may not have checked his e-mail yet to know that you sent it. Perhaps you can send him a message on Steam, if you're friends, and let him know that you've e-mailed the gift, so he should check there to pick it up and accept it. I wouldn't get too worried about it though. As the FAQ says, "The submitter and winner(s) of the giveaway have seven (7) days to complete the gifting process. This includes the activation of the gift on the Steam account of the winner." After that one week period if it's not activated, you can contact Support here and see what they can do to help.