Gangjee fell from 10th overnight.
The other Indian who made the cut, Shubhankar Sharma, shot a second successive 69 to finish tied-24th, up from 36th.
Gangjee, who was in the running for a top-10, had three bogeys and two birdies in his 72, while Sharma shot a bogey free 69.
Australian Jason Norris kept his cool to sign for a closing five-under-par 67, claiming the biggest victory yet in his 21-year professional career with a convincing four-shot win at the tri-sanctioned Fiji International.
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Norris takes home a winner's prize purse of USD 195,421 and moved to seventh place on the Asian Tour Order of Merit, courtesy of his victory at the AUD 1.5 million (approximately USD 1.14 million) event.
Young Thai talent Jazz Janewattananond fired the week's lowest round score of 64 to grab a share of second place alongside Australian duo of David McKenzie and James Marchesani, who closed with rounds of 67 and 70 respectively.