As your domain does not have any nameservers, it is not recognized by CloudFlare. So, please update our nameservers and then you can add your domain name.
Please login to your account, click on your domain name, under "Advanced Options' click on 'Modify Domains Setup' and here under the tab 'Nameservers' add the nameservers as follows and click on 'APPLY NOW"
ns-canada.topdns.com
ns-usa.topdns.com
ns-uk.topdns.com
Once done, you can add the domain name at CloudFlare and then once you get CloudFlare nameservers, follow the same steps above, remove our nameservers and add CloudFlare nameservers