SG's wrong "my games" list

Sync.

This is a known issue with free weekends and guest passes. All that can be done is for the user to remove any game content they may have on their computer and resync their SteamGifts account. It can take up to two weeks for Steam to update the user's library to reflect they do not own the game, however. Sadly, this is a problem on Steam's end and we can't change it.

To prevent this happening in the future, manually sync your account mid-week, like Tuesday or Wednesday. This will reset the 7-day sync to work on the day of the week you last synced, so it won't sync on the weekend unless you do it manually.

Yeah this often happens, since it really does show up in your account during the free weekends. Best just wait for it to pass... or sync a day or two before, as bobofatt said.

The account synchronization

Just wait it out and re sync.