How do you report hours that vary week to week? - any advice?

My hours change every week at my new part-time job and I am afraid of reporting wrongly. Sometimes my paycheck is late by a week. Who can I ask without risking my claim?

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

Thanks for writing this out. I went through something close to it 10 months ago, and it settled down once I kept a simple log of every call and form.