The Scots lost their final warm-up Test 19-16 to France and Cotter believes the run-out in Paris will help his side in their World Cup opener against Japan.
"It certainly went up a level and was a very physical game against a very aggressive defence," he said.
"It was a big game with some pleasing things but things we need to work on."
Scotland went in 9-6 at the interval at the Stade de France thanks to the boot of Greig Laidlaw but lost momentum on occasions with problems at the set piece and losing line-out ball.
"We didn't get ball and when we did it wasn't clean," said Cotter who was in charge of Scotland for the 16th time.
"Despite that, I thought the players defended really well. The guys put in some big hits. Sometimes in days like that if you don't have the ball then you make up for it in other ways. That means you're adapting."
Cotter had special praise for John Hardie in the week the New Zealander picked his fellow countryman for Scotland's World Cup squad despite only having played an hour of rugby for the national side.
He said: "Crikey, John added an edge. He was very effective and got through an enormous amount of work.
"This sort of thing inspires people. He's a class player. We've got some class players and there are some class players that didn't make it."
Scotland's attention now turns to the World Cup and the opening match against Japan on 23 September, followed by games against the United States, South Africa and Samoa.
And, while acknowledging more work needs to be done, Cotter says there is a determination ahead of travelling to England for the finals.
"We're getting better," he said. "We got a reminder that we need to work on our line-out. I thought our scrum was better.
"I think we're showing agility on the field - both mental and physical. We're lining up for the arm wrestle, which is good.
"We're showing a little bit more explosiveness around the contact areas but we need to develop a bit more confidence. We want to do really well in this World Cup and the players are determined."

The Manchester Evening News reported it related to a councillor who admitted making indecent images of children.
Mike Owen and two senior officers have been suspended following an external review of the case, a spokeswoman said.
Council leader Rishi Shori said the suspensions would allow the three to "focus on responding" to the case.
He said they were "a neutral act".
The council had commissioned the review by childcare expert Malcolm Newsam after it "received allegations that there were failures to act appropriately in following safeguarding procedures in respect of an individual case," he added.
Deputy chief executive Pat Jones-Greenhalgh will replace Mr Owen until the council's own investigation is concluded, the authority's spokeswoman said.

He is one of 249 men suing the Catholic Church over alleged historical sexual abuse at St William's residential school in Market Weighton.
Only one man out of five initial cases heard at the High Court in Leeds has been awarded compensation.
In December, a judge ruled in favour of one claimant and ordered the church to pay Â£14,000 in damages.
At the same hearing, His Honour Judge Gosnell dismissed three other claims.
More on this and other East Yorkshire stories
In January 2016 the former head of St William's James Carragher was jailed for the third time after he was found guilty of sexually abusing boys.
Carragher, 75, had already been sentenced to 21 years in prison for sexually abusing boys and was jailed for a further nine years in January.
He was jailed for seven years in 1993 and a further 14 years in 2004 for offences he committed at St William's, which closed in 1992.
Co-defendant Anthony McCallen, 69, a former chaplain at St William's, was sentenced to 15 years in prison for a series of historical sex offences.
He was acquitted of eight other charges at the same trial.
The De La Salle Brothers, a Christian order of lay teachers, which ran the school in conjunction with the Diocese of Middlesbrough, has apologised "unreservedly" for the abuse.
Another set of compensation claims is expected to be heard in late 2017.
Scotland head coach Vern Cotter says his team are "lining up for the arm wrestle" and are showing more "explosiveness" ahead of the World Cup.
[NEXT_CONCEPT]
Bury Council's chief executive has been suspended over claims he and others failed to follow procedures in their handling of a safeguarding case.
[NEXT_CONCEPT]
A man who claimed he was abused at an East Yorkshire Catholic school has lost a legal action for compensation.