The team have a friendly against Peru on Friday before flying out to America to continue their pre-tournament training.
The Everton defender told reporters: "It was an important week last week, getting out to Portugal to get a few more sessions under my belt, and we had a really good session today.
"It is all about momentum. If we can get some decent results in the friendlies we have got before the tournament, confidence will be high.
"People may be playing down our chances but momentum is a fantastic thing in football. The lads are really positive."
England will also face Ecuador and Honduras before their opening game of the tournament.