Help

On your giveaway page, click "delete giveaway".

Yes, you would need to have those 3 copies of the game to giveaway. If you don't, you can go to the giveaway page and click the delete giveaway button.
edit:But, you'll lose all of your giveaway slots, so as David said, you should ask support to remove them and give back your giveaway slots.

Just select your giveaway and click delete.

thanks deleted