Internship schedule making late to college class?

During the interview at a vet clinic I provided a course schedule for chemistry that meets in the evenings which they were fine with. Monday Tuesday Wednesday and Thursday at 6. It’s about a 30 minute drive. But they put me on the schedule to work after 5:40 when they close to clean the facility, because no one else wanted to work these shifts.I’ve talked to them about it but I hope it doesn’t become a regular thing. I don’t know what to do. I have to keep this internship for a year and half to get training for the vet tech program.