Wage reporting when hours change weekly after 15 years as a graphic designer

I picked up part-time shifts as a graphic designer and I am confused about how to report them. 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. Who can I ask without risking my claim?

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