The best way to approach the interview is by being forthcoming about your situation. You need to demonstrate strong reasoning for deciding to study in the USA. It would help if you focused on why you chose the program and how you plan on using the knowledge you will gain to achieve your goals. Suppose a question comes up about precisely whether you will return after graduating. In that case, you could answer it by sharing that depending on the situation – you will either return to Turkey or your home country (if that is what you intend to do).
Regarding your sponsors, they may ask you about your agreement with them – whether it is a loan or not. Typically, you won’t have time to show the actual letter of explanation, so be prepared to communicate what’s in it verbally.
The US Visa Officers are looking for candidates to communicate their reasoning powerfully. Being well-prepared and confident will be crucial to your success.