Re: How to add c-panel after you paid for the service?
It is unclear if you purchased a cPanel plan. If you still need to do so just make sure you're logged in to the same account when making the purchase.
The plan would be listed under Hosting on your My Products page. When accessing for the first time the plan would need to be set-up, where you can add the domain. If the domain and hosting are in the same account it should connect with the proper DNS settings automatically.