Game already exists in your account

sync your account

It will show on your Recently Played for a while now, and until it drops off that list in a few weeks, there is nothing you can do.

Synching the account isn't working for me either. All the stuff that was free last weekend is still listed as owned, even though it's not, and I never downloaded any of it.

Is a known issue. Sync the account every day, eventually it will be fixed. The games can be up to 2 weeks in the SG account.

Go to account details in steam and you should be able to remove it their if XCOM is still their and after that sync your account.