unexpected first time interview what to do

Hi, everyone, I am a sophomore studying international commerce at a target school of my country. I've had a startup internship where I was responsible for analysing KPIs in excel and making presentations about the outcomes. Just recently I applied for an internship at a boutique m&a advisory firm just for the fun of it and I got called to interviews at their office and I am still kind of shocked. I bought wileys technical interview guide and after a couple of hours, i am really overwhelmed by it. I have read some posts here about interviews but I would really appreciate any comments about how in general ibanking or m&a interviews are. If interviews are like what I have read so far, chances are I am gonna fail but no worries i am going to do my best for 5 days. Any recommendations on how to best use these days are very much welcome. Ty all.