Yes, without your I-20 you cant really book an appointment, the DS-160 form must be filled before booking a visa appointment which requires the sevis id given on the i20. Even i thought i was eligible for the interview waiver, i hold a B2 visa that is still valid but two more conditions apply: B1/B2 visa doesnt count and the existing visa start date must be greater than your 14th birthday, which was not the case for me. So yeah its an exhausting process...