Well, first, make sure that you go back over your schedule and account for any lunches where you had to clock out and any time you clocked in late or clocked out early. Then, if your math adds up, speak to your department manager first and see what they can do to help you figure it out. It's not on them to pay your check out, but they can probably figure out where the missing hours are and help you get them claimed if need be.

If your dept. manager is not helpful and you still feel you're justified in getting those hours, go to HR or your store director and see what they can do to help you.