MERRICK - Second to the game itself, those side-splitting commercials between Super Bowl plays are why millions of people tune in, and this year, a Long Island filmmaker is behind one of those ads. Zachary Borst, 26, of Merrick, found out yesterday that he won the Chevrolet Super Bowl Ad contest. He beat out nearly 200 competitors with his commercial about an ecstatic graduate who gets a brand-new Chevy Camaro from his parents. Borst says he owes his success to the performance of his stellar cast, who gathered with him in Floral Park today to celebrate.