How do you report hours that vary week to week? (Nashville)

I picked up part-time shifts as an IT help-desk technician and I am confused about how to report them. It has been weighing on me all week. The form asks for gross earnings, which I do not see until later. 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.