Should I stay in my internship or should I leave?

So I really don’t know what to do right now. I know this is long, but please power through. I need outside opinions.
I interviewed for this job in December last year and was offered the internship. At the time, I had no other options even remotely possible and registration was the first week of January so I accepted. Two days before I started, I received an email from another company that I applied to (and for an internship position that is better suited to my chosen field). They said they were interested and wanted to interview me. A day after that I received another email from yet ANOTHER company; basically it seems like all these places want to choose their interns weeks after registration and the start of classes. Since it was only confirmation for an interview, I told them I would interview but didn’t tell my accepted internship. Yesterday I went for the first time. They are a small company and are really nice, but I found out that apparently I am required to work 15 hours a week. This wasn’t noted on their application, job posting, or in the interview. They didn’t specify I had a minimum number I needed. This is a problem because essentially this is my schedule as of now for Monday and Wednesday with school and the internship.
Mon:
8:30 – 12:30 work
1:30 – 3:00 class
3:30 – 5:00 work
Wed:
8:30 – 12:30 work
1:30 – 3:00 class
3:30 – 5:00 work
5:30 – 8:00 class
Friday is the same but I just don’t have to go back for the 3:30–5:00 block. I couldn’t put my hours on other days because literally I am in class from 9:35 to 7:30 all day with only an hour and a half gaps. I go to a very rigorous university and this doesn’t even factor in time for group assignments, readings, and studying. This is also a lot of extra driving for me. I may have felt different if I was getting paid, but they are only giving me $1,000 for the ENTIRE semester. That’s only a couple hundred dollars more than all the money it would cost me for gas to drive there and back multiple times a day (in a major city’s traffic, think like Chicago level big). I made more than that at my on campus job where I worked less hours and had time to do my homework at my job. By the time I got home last night, I was incredibly tired and stressed because I still had a bunch of readings to do, and it’s not even deep in the semester yet where I would have more work. My grandparents really want me to quit……..they said they would even try to give me money if they needed to……..I’m not sure what to do. I really don’t like the situation, but the people are nice and I need something on my resume. Also, if I don’t have this internship, I will be 1000% broke. I don’t like taking money from my grandparents and having the little bit from my job on campus gave me a level of independence that I no longer can enjoy. I feel guilty now for going and making it seem like I was ready to be there for long term. Going in, I was, and my first day wasn’t OVERLY busy….but I can see this schedule messing me up in the future. It is my last semester in school, and I have made all As for the past 4 semesters which is nearly unheard of at my school. I’ve been doing well and I feel like this might mess up my final GPA. I have other options, but they are far from guaranteed. They are nice people at this company, and it’s not directly related to my future career plans but it’s kinda sorta related…..I haven’t signed a contract or anything.

Should I stay or should I leave? And if I should leave, how do I do that without seeming like an asshat? I really feel bad about this….I don’t like going back on my word and they’ve already got me a parking pass and login and stuffs…..and I already started on some work…..