Hi Redstar,
Thanks for posting your question. I'm more than happy to assist you today. I've looked into your account and seen the add-on domain's registration went through this morning. It can take up to 24 hours for the domain to propagate, and after this time you can use it with your webhosting account. Once the domain propagates you'll be able to access it.
If you need further assistance please feel free to contact us.
Thanks!
Tim S