When Previewing a Donation Form's Thank You Page, the content displayed will be that of the generic John Doe. This is expected behavior, due to preview mode not having any specific donor information to pull from. Rest assured, then when on the front end of the Donation Form, after a donor makes a real donation with an actual credit card, that particular donor's information will be pulled into the Thank You Page. If you'd like full assurance of this experience, you can navigate to the Donation Form's URL and record a real transaction with your regular constituent record that you can then refund afterwards.