Germany defeated Denmark to win the group without ever hitting top gear, Lukas Podolski and Lars Bender scoring amid several wasted opportunities.
"We had three or four very good chances and missed that killer instinct... that would of course have made the whole task much easier," Low told a news conference after his side's third consecutive win at the tournament.
"We had a job, we made it, we got through the group so we're very satisfied. I think we can get a little bit better and we need to do that in the next games."
Low complained his team had left too many spaces in midfield and defence on occasion, allowing Denmark to slow down the game.
"We could improve on that because Greece will be similar. They're going to try to take the tempo out of the game," he said.
"They can really defend well, they really throw themselves into it whenever it's dangerous, they're right there. They're very hard and it's like you're just biting on a rock."
Low had earlier told German television that Germany were capable of being more focused against Greece in Gdansk on Friday.
"We need to force the next opponent to their knees and then we'll see what happens after that," he said.
Midfielder Sami Khedira echoed Low, saying: "We're going to have to get used to it and not complain when a team pack their defence."
Bender, who was only playing because of Jerome Boateng's suspension, said the goal had been a wonderful present.
"It was a bit of luck that the ball came to me but you don't think a lot about it, you just shoot it in," he said.
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