The left-back, who is the youngest player fielded by any side at Euro 2012, came in for criticism from Oranje boss Bert van Marwijk for his performance against Northern Ireland
The 18-year-old started Saturday's 6-0 victory over Northern Ireland, but was criticised by coach Bert van Marwijk for occasional lapses of concentration.
"People make mistakes," Willems said to reporters. "Often I rely on my pace, but I will pay more attention [to my opponent]."
The PSV man is likely to start the Netherlands' Group B opener against Denmark on Saturday, with the only other competition for the left-back spot, Stijn Schaars, also unproven at international level.
Willems made 20 league appearances for the Eindhoven outfit last season, scoring one goal.