Giveway for not so unlucky people

Yes. Public giveaway can NOT have rules.

Private giveaways can have rules, BUT you need your rules approved by SG support / SG mods first ;)

What you could do now:
1) Go through with the giveaway and give the game to the winner, even if he does not match your requirements.
2) Delete the giveaway, get your rules approved, create a new giveaway
3) a) Go through with the giveaway and do not hand out the game if the winner does not met the requirements - however you will get a "not received"
3) b) same as 3)a), but ask support for a re-roll. but they will probably say "no", if you did not get your rules approved first.

Public ones can't have rules, private and group ones can have rules when they are approved by the support.