Can't enter giveaway because I owned the game from free weekend, how can I remove it?

Sync your sg account.

http://www.steamgifts.com/sync

well to prevent this from happening dont sync during free weekends. you have to wait for the free weekend to end then sync again in order for it to remove from account. the same thing sometimes even prevents people from buying from steam, in terms of dumb things its on an epic level of screw ups lol

Note that if you end up playing the game during free weekend, syncing will not remove the game from your owned list for another 2 weeks.