How do you report hours that vary week to week? after 8 years as an HR coordinator

I picked up part-time shifts as an HR coordinator and I am confused about how to report them. It has been a long 13 weeks. 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.