If you use the automated process for site supporter, you do not need to do anything special. It's automated so it does everything for you.
The only reason you would need to include your username is if you did not follow the instructions for the automated tool and manually sent money into the paypal account or mailed it to the post office.
You may also view your expiration date via your UserCP/Paid Subscriptions link. This should give you the information you need to know if what you did worked.
Please let us know if there's anything else we can help you with.