Should I quit my summer job and focus on summer classes?

I'm an engineering student, I started a summer project job/internship, which means it's for a month. I was told it would only be a few hours a day and that it was easy, so I jumped on it since my job as a maintenance worker on a golf course was physically demanding for very little pay. However, my boss ended up being a total a**hole, it's eight hours a day, and the job is just as physically demanding as my last job and only for a dollar more an hour. I take two classes at the moment and they are both very difficult, I also play college golf, but with this internship, I hardly have time to study, I can't workout or practice during the week at all, don't have any free time, and I'm very stressed out. It's only been a week but I'm already wanting to quit, to focus on what really matters for me.