The London Irish centre described the build-up to the match as the "worst week I had known in international rugby".
Catt and England team-mate Lawrence Dallaglio, whose autobiography is also being serialised in the Sunday newspapers, have been widely condemned for going public with their views.
But while admitting the timing of his comments was regrettable, Catt insists Ashton was culpable for failing to provide leadership early in the tournament.
"The whole timing of it was not very good," he told Sky Sports News.
"I had no intention of that (detracting from the team getting to the final) happening.
"It was not a personal attack, it was more of how I felt at that particular time in the tournament.
"I felt differently day by day and that was the only way I could express myself.
"I really wanted to be honest about exactly what was bugging me. It was the truth and how I felt.
"We hadn't had a great build-up and after being beaten 36-0 (by South Africa) we weren't happy and the management weren't happy.
"A few words were spoken and Brian stood up and turned the thing around.
"What we needed tactically I felt was a lot more from Brian. That is how I felt at that time of the competition.
"Once we sat down and had our meeting after the South Africa game we played exceptionally well and got to the final."
Catt insists Ashton, whose position is being reviewed by director of elite rugby Rob Andrew, should remain in the England set-up - although he is not convinced his best role is as head coach.
"I've got the utmost respect for Brian after working with him for 15 years," he said.
"The last thing I want to do is throw that away through 10 lines written in my book.
"Brian is one of the reasons I'm sitting here talking about an autobiography, so I want to focus on the positive side.
"We desperately need to keep Brian involved - I'm not sure whether that should be as a head coach or senior coach.
"He brings a freedom to the park that youngsters coming into the game now will thrive on. It's vital he stays."