Do I need to quit my job to get 3 As?

I have a part-time job, and it's not a very enjoyable one. Being in the food service industry, it is very high-stress and was badly managed for the first several months I worked there. I find myself actively thinking about work when I'm not there and wake up to messages from my colleagues asking me to cover shifts or do accusing me of doing something wrong. I've worked there for nearly a year, and I have had a hard time getting my managers to listen to me about cutting my hours back for school. They can mess me around as much as they like because I am on zero hours; for example, in the summer I worked five hours in two weeks. A few days later I did 49 hours over 7 days. I have told them I can only work for one weekend day but they continue to schedule me over time. I want to quit desperately to focus on school, but I don't know how and I need money to pay for so many various things. I don't have another source of income to fall back on. I'm paying my mum back slowly but surely for my laptop, I'm paying for a trip to Iceland, and I'm paying for a car/driving lessons. So I need money. But I also need three As to get into the course I want to do more than anything. What do I do?

I have a part-time job, and it's not a very enjoyable one. Being in the food service industry, it is very high-stress and was badly managed for the first several months I worked there. I find myself actively thinking about work when I'm not there and wake up to messages from my colleagues asking me to cover shifts or do accusing me of doing something wrong. I've worked there for nearly a year, and I have had a hard time getting my managers to listen to me about cutting my hours back for school. They can mess me around as much as they like because I am on zero hours; for example, in the summer I worked five hours in two weeks. A few days later I did 49 hours over 7 days. I have told them I can only work for one weekend day but they continue to schedule me over time. I want to quit desperately to focus on school, but I don't know how and I need money to pay for so many various things. I don't have another source of income to fall back on. I'm paying my mum back slowly but surely for my laptop, I'm paying for a trip to Iceland, and I'm paying for a car/driving lessons. So I need money. But I also need three As to get into the course I want to do more than anything. What do I do?

Sorry to be patronising, but you're a child. You don't HAVE TO PAY for "various things" Driving lessons can be postponed, so can the trip, and you can just work next summer to pay your mother back. Think about your future for crying out loud.