Wage reporting when hours change weekly after 13 years as a delivery driver

My hours change every week at my new part-time job and I am afraid of reporting wrongly. I have been trying to stay organised about it. The form asks for gross earnings, which I do not see until later. Did anyone get an overpayment notice from a mistake?

Report honestly and keep your stubs. An honest small error is much easier to fix than a missing report.