There is no "other pay" box on a W-2. The only place to enter income other than allocated tips on a W-2 in in box 1. Where exactly are they entering the income on the W-2? Are they withholding social security and medicare taxes from it and paying the other half just as they would with your wages?
It sounds like they are treating you as an employee for all your income. If so, you are no longer "self employed" and would not file a Schedule C for self employment income.
