How do I handle running a store for a salary that's too low?

The whole store lands on you, sales, theft, staffing, corporate's endless demands, and the salary does not come close to matching the stress. Carrying all of that for pay that ignores the weight is genuinely unfair, and you are right to feel the gap between what is asked and what is given. Start by getting honest about what is actually yours to carry. You are responsible for running the store well. You are not responsible for fixing every problem corporate creates or controlling every thing outside your reach. When you take on responsibility for things you were never given power over, you drown. Draw that line clearly and defend it, in your own head first. Then face the pay squarely, because resentment that just sits there poisons the work. Either make the case for what you are worth, with the numbers you deliver, or look at what else your skills could earn elsewhere. Running a store is real management experience that transfers. In the meantime, protect your hours and your health from a job that would happily take everything. You can run the store well without letting it run you into the ground.