How do you report hours that vary week to week? after 15 years as a nurse's aide

I work some days through a staffing agency while still certifying. I have read a lot of threads here and could not find my exact situation. The form asks for gross earnings, which I do not see until later. Did anyone get an overpayment notice from a mistake?

The claimant handbook has worked examples for part-time pay. Mine was clearer than the phone line.