How do you report hours that vary week to week? - what worked for you?

I work some days through a staffing agency while still certifying. It has been a long 13 weeks. The form asks for gross earnings, which I do not see until later. Did anyone get an overpayment notice from a mistake?

Thanks for writing this out. I went through something close to it 9 months ago, and it settled down once I kept a simple log of every call and form.