Jacques Lapointe told the public accounts committee that he considered the board "adequate proxy" for reporting to cabinet.
"We should have been clearer on that," Lapointe said after questioning by New Democrat Clarrie MacKinnon.
The Treasury Board consists of some members of cabinet.
Last week, Lapointe said the NDP government knowingly delivered a budget last spring that included a deficit forecast of $211 million, when the actual figure was $238 million. Lapointe said his office urged the Finance Department to inform cabinet and that was done.
Premier Darrell Dexter has denied knowing anything about the mistake and has never sat on the Treasury Board.
Former finance minister Graham Steele was a member of the board at the time. But his successor, Finance Minister Maureen MacDonald, was not.
A motion to have Steele, MacDonald and the chairman of the Treasury Board appear before the public accounts committee was rejected on Wednesday. All five New Democrats on the nine-member, all-party committee voted against the motion.
Liberal Andrew Younger, who put forward the motion, said he's not surprised it wasn't approved.
"Obviously the NDP has something to hide," he said. "Otherwise they'd be willing to show up and defend themselves."
But MacDonald rejected Younger's assertion, saying she answered questions from reporters about it last week.
"There's no reason for me to come and spend two hours confirming what I've told you last week and which the auditor general has said today was an accurate representation of what occurred," MacDonald said.
"I have nothing to hide. ... There's nothing left to tell."
Finance Department staff are scheduled to appear before the committee next month, she added.
Lapointe has said the $27-million discrepancy was "significant enough to be corrected" before Steele delivered the budget. He also said the error could have been corrected before the budget was presented.
Steele's constituency office said he had no comment.
MacDonald disputed that there was enough time to change the budget.
"The decision was made that there wasn't enough time," she said. "Once you change one number, it has a ripple effect."
Progressive Conservative Leader Jamie Baillie said MacDonald's explanation isn't good enough.
"Let's call it what it is. We have a dishonest budget and that's wrong," he said. "There's not a cut-off date for telling the truth, and that's what stinks about this whole thing."