You really have to take a step back and take a deep breath. Realize that this is a crappy part-time job and it is not a big deal. You have to take the attitude that they need you (which they may or may not, doesn't matter), that if you are a good worker you can get a job anywhere. Take the high road.

I had a crappy job where the boss would always ask you to work extra. We would fill in our own schedule. We had a minimum amount we had to work, but we would always get asked to work more. I would tell my boss that that was it, I filled out the schedule and I had plans for the other time. Because I was a good worker and reliable, I could get away with it. Your problem may be a bit different where you are not getting enough hours. If you are a good and reliable worker, you should be able to negotiate more hours, But...

What you need to do get a back-up plan. Look for a second job, but go looking for the job while you still have the first job. You are then in a position of strength. You can tell your prospective employer that you have a job but are not happy with the amount of hours and you are considering a new job. It's like trying to find a girlfriend, you look a lot more attractive when you already have one. When you quit, if you do, do it right, give notice, take the high road.

You have to not take anything personally, I know that is hard, but you have to react in a detached, business like manner. That way you will not react emotionally and make poor judgments. Have a clear plan in your mind before any encounters with the boss.

Look at all the experiences as a type of training for later in life when it really matters with real jobs