Gambari was speaking to reporters in Singapore on the sidelines of an annual summit of leaders from the Association of South-East Asian Nations (Asean) and neighbouring countries
His comments came after a UN panel meeting in New York strongly condemned Myanmar's human rights record.
The UN general assembly's human rights committee overwhelmingly passed a resolution condemning the September crackdown and calling for the release of all political prisoners in Myanmar.
Myanmar's ambassador to the UN, Kyaw Tint Swe, called the resolution "unacceptable" and said it was part of a "systematic disinformation campaign against Myanmar".
The resolution, which is not legally binding, also calls on the Myanmar junta to work with Gambari to achieve "effective progress towards the restoration of democracy and the protection of human rights in Myanmar."
Gambari himself had been due to address a meeting of 16 Asian leaders in Singapore on Wednesday, but the briefing was abruptly cancelled following objections from the visiting Myanmar prime minister.
The UN envoy said he was disappointed at the decision, but had nonetheless held informal talks with several delegations.
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"It didn't turn out quite as it was planned but I would say that my visit here has been extremely worthwhile," he told reporters.
"I had a tremendous opportunity to meet with so many delegations, so many leaders."
Asked what measures were needed to help him achieve his mission to push for reforms in the military-run state, he said his role needed to be "beefed up in terms of its effectiveness" but did not elaborate.
Lee Hsien Loong, the prime minister of Singapore and host of the summit, said he had explained to the Nigerian-born diplomat the circumstances of the abrupt cancellation.
"I thanked Dr Gambari for making the trip. I explained to him the circumstances and how they have changed over the last few days and the position as it stands today," he said after talks with Gambari.
Lee said that Asean had nevertheless given their backing to Gambari's efforts to push Myanmar towards democracy after four decades of military rule.
"Most of the Asean leaders felt Myanmar could not move back, cannot stay put, and has to move forward towards national reconciliation," he said.