The 2008 champion from Portrush warmed up for next week's Open at Royal Troon by finishing on nine under and five behind winner Alex Noren of Sweden.
McDowell picked up birdies at one, six and 16 but bogeys at 15 and 17 ended his title hopes.
Padraig Harrington was six under after a 71 while Belfast's Michael Hoey was back on four over following a 72.
Noren clinched a one-shot victory over nearest challenger Tyrrell Hatton.
McDowell, who has slipped to 78th in the world rankings, goes into the Open in improved form and having already played two practice rounds at Troon last weekend.

The Holy Trinity fighter had a 3-2 majority win against the World and European light-welterweight title holder to reach the quarter-finals.
Monday's victory also secured his place at the World Championships in Hamburg, Germany in August.
Belfast flyweight Brendan Irvine is also through to the quarter-finals.
The Rio Olympian beat Turkish opponent Bathuhan Citfci on a unanimous 5-0 decision to advance to the last eight, the victory also securing his place at the World Championships.
McComb, who easily dealt with Czech Erik Agateljan in his 64kg opener, had previously defeated the top-ranked Russian at a multi-nation tournament in Dublin in April.
However this victory is much more significant, the fighter tweeting "nothing won yet, I'll just keep trucking" after his great win in Kharkiv.
He now meets England's Luke McCormack in the quarter-finals.

sportscotland says it has yet to decide where the cuts will fall amid concerns that elite athletes could suffer.
The cuts are being blamed on reduced government spending and a drop in National Lottery ticket sales - a major contributor to sports backing.
Governing bodies are bracing themselves for potential job losses.
About 60% of funding is made up from Scottish Government money, with lottery sales making up the rest.
In the year ending 2015, total revenue was £65.1m, which is divided up and awarded to 52 sports.
By the end of next year, that figure will have fallen to £51.8m - a cut to the Scottish sporting budget of 20% in just three years.
sportscotland chairman Mel Young said: "It's heartbreaking to me because I know the effort the sport governing bodies and the community that's around it; the volunteers and the mums and dads.
"And, to have to say that we're having to cut some money back is, I believe, not the right way to go."
Former badminton player Susan Egelstaff, a double bronze medallist at the Commonwealth Games [in 2002 and 2006] and an Olympian, fears the cuts will have "a huge impact".
"What that means in the future is that Scotland will be constantly playing catch-up," she said. "It's almost impossible to catch up if you fall too far behind the leading nations."
The Scottish Government said sport and physical activity play a "key role" in a healthy Scotland and that "significant" investment would continue in those areas.
"Having successfully delivered the Commonwealth Games [in 2014] we are now focusing on protecting or raising investment in areas intended to decrease health inequality and improve life chances, and the small reduction in the sport budget allows us to support those priorities," Minister for Sport Aileen Campbell said.
"There is on-going support for active lifestyles through capital investment in cycling and walking, and over the last 10 years we have invested £168m in sport infrastructure - from grassroots to the elite performance which has increased the facilities and opportunities to get people active and achieve on the world stage at both the Olympics and Commonwealth Games."
Graeme McDowell carded a final-round 71 to end the Scottish Open at Castle Stuart in joint 10th.
[NEXT_CONCEPT]
Belfast boxer Sean McComb is one fight away from a medal at the European Championships after stunning world number one Vitaly Dunaytsev in Ukraine.
[NEXT_CONCEPT]
Sport funding in Scotland is facing a 20% reduction over a three-year period, a move described as "heartbreaking" by the national agency.