The aggravated robbery left the shopkeeper "clearly traumatised", said Judge Claire Ryan at Whaanga's sentencing late last year.
In his victim impact statement, the man said he didn't suffer any physical injuries and the property was recovered but he was still scared to work in the store, especially at night.
"My wife regularly comes to check on me to make sure I'm okay. I'm not sleeping properly. I wake up thinking about the robbery. Then I can't go back to sleep," the man said in his statement.
He wanted to go back to India for a holiday to clear his head. He set off on that holiday last week but declined to speak to the Herald.
Whaanga was charged with aggravated robbery and unlawfully getting into a car in relation to the incident and was also charged with unlawfully entering a building and failing to answer bail.
At sentencing at the Auckland District Court in November, the Crown argued for a five-year jail term because there was more than one person involved in the robbery, a weapon was used, it was a liquor store, which are targeted too often, and there was unprovoked violence.
The now 20-year-old also had 11 previous convictions.
Whaanga's lawyer said the defendant's age should be taken into account as well as his guilty pleas.
The defendant also wrote the judge a letter in which he said he regretted what he'd done, took responsibility for his actions and was willing to prove he could make changes in his life.
"Mr Whaanga, most people I'm about to jail write letters to me like that. They all come to court saying how terribly sorry they are and how they want to make changes in their lives," Judge Ryan said.
"That is all very easy to say but you have got to do it by doing more than talking the talk but walking the walk. Walking the walk is very hard; it takes a great deal of courage to make positive changes. You have yet to do that."
But Judge Ryan said she could see Whaanga took responsibility for what he'd done and not everyone who came before her told her that.
She sentenced Whaanga to three years, two months imprisonment for the aggravated robbery, 12 months for unlawfully getting into a car, eight months for failing to answer bail and one month for unlawfully being in a building to be served concurrently.