A learner driver was on the right side of the road when his car hit a pedestrian in a supermarket car park, he told a court.
Prosecutors allege Timothy Higgins of Blackwood, swerved to hit Christopher Gadd, 48, after an argument.
The 22-year-old denies manslaughter at Cardiff Crown Court, following Mr Gadd's death in March.
He also denies causing death while driving without a licence and causing death while driving uninsured.
Mr Higgins said he was not admitting responsibility when he said "My life is over, I've killed him, haven't I?" in the Sainsbury's car park in Pontllanfraith, Caerphilly county, after it happened.
He admitted there had been an altercation outside the store and he "might have shown a V sign" to Mr Gadd and his brother as a "brush off".
The defendant added he had locked the doors of the Landrover Freelander he was driving because he was "scared".
"Anything could have happened - he could have punched the window, he could have had something in his hands," he told the jury.
Mr Higgins also said there were no L plates on the vehicle but he thought he was driving in accordance with his provisional licence because a qualified driver was sat alongside him.
The trial continues.