After you sign up, you have to go back to the event page. It should give your key at the bottom of the page.
If you get 'You already got a key', please email
contests@onrpg.com with the subject "Turf Battles" and tell me EXACTLY what you did (from the first visit to the page, to registering, etc). I will do my best to help everyone but I have to know what it is that is going wrong exactly.