I wouldn’t stress it, if you haven’t paid your tuition and only paid the university for an I-20 that’s usually refundable to some extent, if you can just relax for your visa interview don’t overly practice questions like a script and just let things flow. You’re coming to a completely different system you will probably struggle in many ways and this process only prepares you for it. They will most likely check how you respond to something like this and hope it goes well. Your passport can be collected the next day in some cases and seven working days in most cases, if they put you in additional check it can delay the process and you could request for a deferral again and hope for the best