How do you report hours that vary week to week?

I picked up part-time shifts as a customer-service rep and I am confused about how to report them. I have read a lot of threads here and could not find my exact situation. Sometimes my paycheck is late by a week. Did anyone get an overpayment notice from a mistake?

I estimated and then checked my pay stub. When there was a small difference I wrote to the agency to correct it.