first of all my congratulations to your internship - this is already a big deal!
Don't think about the conversion rate. Of course, the current situation will have impact on the conversion rate. McK will simply increase the performance bar for the conversion.
So your job is to become a top performer and get into top 20% of summer interns.
I have developed a program "get ready to the first 100 days", which will help you to learn and master consulting skills even before you get into the company. This will help you to become a top performer and secure your full time offer during the internship.
Happy to answer your questions and help you!