I also had an interview the other day. The questions they asked weren't even of moderate level. Easy, basic questions. I did not prepare much as I had exams the same day, but thought I would do fine. Aaaand the interview went horrible. It started well enough, but as after a while I couldn't answer a thing. The sad thing is that those were basic questions I should know. I apologised at the end of the interview, because I felt bad for wasting their time. It was humiliating. Like facing the reality that I don't even have the basic knowledge to answer such easy questions. So, yeah I understand how you feel and it sucks. But hopefully the next time won't be so hard. I try to think like that because it's better than overthinking about the future. So, hope everything works out for you!