“Maybe in Russia there were times, towards the quarter- and semifinal, when I wasn’t as sharp as I wanted to be,” the 27-year-old Kane added.
“It’s about managing the squad, making sure everyone is feeling as fit and sharp as possible.
Asked if a desire to leave his club Tottenham Hotspur had affected his performances for the national team, he replied: “Absolutely not.
England, who have four points from two games, must beat group leaders the Czech Republic at Wembley on Tuesday to qualify for the last 16 in top spot.
“We all pride ourselves on not conceding, from front to back, and now I feel we can get better in the attacking third and be a bit more fluid and a bit more free and create a few more chances.