I know exactly what you are going through. I had to take a class this summer and cut out 15 hours of work. Luckily, my boss realizes that my school comes first and foremost. I think you got some good advice. Maybe instead of messing up your work schedule you should go to the first day of classes and talk to the professor. Many are very good about letting people who are about to graduate practically get away with murder. I know my school is like that since our 4-year graduation rate is relatively low and they want to get us outta there
I have a feeling the prof will let you work an Independent study thing out. Its not like you're a freshman who has no idea about college work.