How do you report hours that vary week to week? after 8 years as a warehouse supervisor

I picked up part-time shifts as a warehouse supervisor and I am confused about how to report them. This is my first time dealing with any of this. 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.