The Three Lions captain bagged the second goal in a 2-0 win over Poland at Wembley that earned Roy Hodgson's team automatic qualification for the tournament.
Wayne Rooney had opened the scoring just before half-time, but the visitors had several chances to shock the hosts, who couldn't afford a draw, and Gerrard conceded England, who gave away possession too easily at times, must improve their ball retention to beat the world's best.
"The big lesson is to play better in the second half," said the Liverpool player. "We must keep the ball better when it gets tough.
"But at times in the last two games we were fantastic. Tonight, we started really well and we are getting better defensively.
"We know there is a great togetherness in the squad, and that is all that matters. We performed under tremendous pressure."
Rooney predicts England joy
Meanwhile, Rooney said patience had been key to England's success against the Poles, who featured prolific striker Robert Lewandowski and arrived with nothing to lose as they were already out of the qualifying race.
"A big part of our preparations was being patient," said Rooney. "We knew they would come and make it tough. We have always remained positive. We have had a great focus and belief."
With the road to Brazil finally reaching a successful conclusion after some disappointing displays earlier in the qualifying campaign, Rooney is adamant England can go to the World Cup confident of making an impact.
"We have some fantastic young players in our team, with some great experience," he said. "It is a good blend, it is good times for England."