Wage reporting when hours change weekly - what worked for you?

My hours change every week at my new part-time job and I am afraid of reporting wrongly. I worked as an administrative assistant before this. 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 last year, and it settled down once I kept a simple log of every call and form.