Wage reporting when hours change weekly - any advice?

I picked up part-time shifts as an IT help-desk technician and I am confused about how to report them. There are 16 people counting on me, so I am trying to be careful. The form asks for gross earnings, which I do not see until later. Did anyone get an overpayment notice from a mistake?

Keep everything in writing and save the confirmation numbers. It made the follow-up calls so much easier.

I estimated and then checked my pay stub. When there was a small difference I wrote to the agency to correct it.