"No excuses. I'm guilty," Verstappen is quoted by De Telegraaf newspaper.
"I was late with the clutch in the anti-stall system," he added, with the crash reminding some of the way the late Maria de Villota also lost control when she was testing a Marussia in 2012.
The incident occurred during a third donut-laden lap of the Rotterdam layout, and Verstappen explained: "Twice it went fantastically, one time there was a mistake.
"It's a learning process. But after everything, this is what I've always wanted -- to drive a formula one car."
If Verstappen is granted a super license by the FIA, Toro Rosso intends to run him on Friday mornings at grands prix later this season.