"The biggest problem, the biggest challenge and the job that gave us most problems and missed the deadline was the velodrome," Mayor Eduardo Paes told reporters in Rio. "The track is practically done. We have 30 to 40 more days of intense work but we are on schedule."
Rio's original plan was to use the velodrome built for the 2007 Pan American Games but that was scuppered after officials said the venue did not meet Olympic standards.
The old one was dismantled for rebuilding in the centre of Brazil and a brand new one erected in Rio's Olympic Park, the main cluster of venues.
Paes, who declared the park open on April 12, said it was 98 percent complete with the tennis centre needing last-minute work. The main courts are ready but temporary seating still needs to be installed, he said.
Paes also announced public holidays on three days during the games, both for the opening and closing ceremonies and on Aug. 18, the day of the men's triathlon event in Copacabana.
Following a strategy used during the 2014 World Cup, officials hope to reduce the amount of traffic by keeping cars off the road and through the use of special traffic lanes for Olympics visitors.
Paes said 260 kilometers (161 miles) of traffic lanes will be used to facilitate the movement of athletes and officials. The lanes will be opened for tests on July 25 and be fully operational six days later.
Rio was last month declared the fourth most-congested city in the world by navigational device manufacturer TomTom.
"We are at the point many people doubted," Paes said. "But we are going well ... 100 days is always a landmark, it's a demanding period and there is a lot of pressure."