The hosts started well in the game on Friday but lost momentum and needed strong performances from their replacements to secure a bonus point in the final minute.
“There are certain areas we need to work on. But it is a good start," Catt told reporters.
"Certain individuals will be disappointed with their performances, but come Thursday, Friday, Saturday, there is a lot of experience now so that they can pull each other through. The whole bench came on and made a huge impact."
England are preparing for a huge game against Wales at Twickenham on Saturday.
“We talked about the pressure the players were under and they dealt with it and we came away with what we wanted," Catt said.
"For us to get that try in the dying seconds is massive for our confidence," he added.
The England players went home for the weekend and Wales beat Uruguay 54-9 to get their campaign off to a good start.
"We need to make sure that defensively we are able to stop the big threats," Catt said.
"It is the biggest game that a lot of the guys have ever played."
England could replace number eight Ben Morgan with Billy Vunipola, who came off the bench to get the last try against Fiji, and the centre partnership of Brad Barritt and Jonathan Joseph also failed to fire.
"It is all or bust for us and for Wales," Catt said.
"They came very close four years ago (reaching the semi-finals) and they won’t let these opportunities slip. They are going to throw absolutely everything at us and vice-versa."
Catt believes the Twickenham fans will help the tournament hosts.
"The crowd against Fiji were incredible," he said. "If we can have the same support against Wales, it will be massive for the team."
(Reporting by Ed Osmond; editing by Ken Ferris)
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