Paid internship with no over time expecting me to work more than 8 hours a day.

I’m currently doing a paid internship for an IT company, during my internship I only get paid for 40 hours per week but all official employees make OT. We’re on day 2 and we’ve already put in almost 21 hours this week and they’re insisting on working into the night. They’re expecting me to stay and not say a word about my unpaid labor and I can’t just leave because they insisted we share rental vehicles