The 44-22 victory set up a quarter-final eliminator against Tonga at Parc des Princes on Friday night, with the winners set to face Australia in Marseille eight days later.
Gomarsall said: "We are going with confidence into the Tonga game - we know it is going to be another hard game, physically.
"We were under massive pressure (against Samoa), and the team showed great character.
"The proof is in the pudding, and we have got to produce the goods again on Friday.
"The important thing for me is we have another good week, and build on the detail. There is so much more to improve."
England saw a 23-6 lead reduced alarmingly to 26-22 early in the second period, but a storming finish when skipper Martin Corry and wing Paul Sackey each claimed their second tries left Samoa floundering.
Wasps star Sackey said: "There was a 10 or 15-minute period when they were camped on our line, and I was getting a bit worried, but I knew our defence was strong.
"We had the buzz. The mood was good all week, and we just hope we can carry that through to the next game."
While the likes of Gomarsall, Sackey, Corry, lock Simon Shaw and flanker Joe Worsley all shone, it was returning fly-half Jonny Wilkinson who guided England home.
His first 2007 World Cup appearance after injury brought a 24-point haul - four penalties, three conversions and two drop-goals - and he took everything Samoa's destructive tacklers threw at him.
Wilkinson said: "We've got the opportunity now to analyse and go forward with a positivity, having won, which is very different to coming off the back of the previous two games (against America and South Africa) when there is disappointment.
"Having won, it does give you a bit more of a positive feel, which is a much more enjoyable environment.
"It was looking like a very tough second half, but we managed to turn it around. We managed to find a path to a win when things looked difficult."