W2 says $50K. Really made $40K + $10K reimburse for miles. Should the $10K have been reported as Income? My gas/repair/insurance cost is $12K. How to capture?

W2 Says $50K.  Really only made $40K.     Why were reimbursements for my business miles paid counted as income?   Even if I broke even. - cost $10K and reimbursed $10K - I am not paying social security taxes, state and federal income tax on the $10K.

How do I deduct the $12K I really spent (gas/insurance/repairs) so that it offsets the $10K and reduces state/fed/fica?

Thank you.