In the United States, race is based on self-identification, not a rigid formula. There is no single "correct" racial category for someone with a Mexican father and white American mother.
Options include:
The U.S. Census since 2000 allows multiple racial selections. Your legal identity: U.S. citizen by birth (jus soli). Your cultural identity may blend Mexican heritage, white American upbringing, and your own synthesis.
Key points:
Embrace the complexity. Your identity is yours to name.