Coop probably has the best advice. Your top priority needs to be your health, and school. If you neglect your health then it doesn't matter what else you're doing, you won't be at your peak; and most guys, even if they end up playing hockey professionally, will end up doing other things after their career is over. Your education will be vitally important later in life, and shouldn't be overlooked. Health and school are the foundation for the rest of your life, and sacrificing either for a low-level retail job or hockey (much as we all might love it) is a bad idea.
Since you really want to pursue hockey as much as you can, it seem like you've already decided it's more important than your retail job, the catch being that it's also necessary to fund your hockey. Ideally, there should be people and support systems in your life that allow you to pursue your passions without worrying about money constantly. Obviously, that isn't a reality for lots of people, and there's no easy answers here. We don't know the specifics of your financial situation, so any advice we can offer on that front would be limited at best. (speaking very generally, I'd recommend seeing if there are any areas in your monthly budgeting that you can cut back in to save money, and also talking to your boss at work about changing your hours to better accommodate your school and hockey)