The London Irish centre's 11th appearance against Australia - an England record - ended in a 43-18 defeat as the Wallabies followed up their 34-3 first Test victory by inflicting a six-try drubbing on Andy Robinson's hapless world champions.
"International rugby is a lot harder than people expect, and when you come up against sides like Australia who are well-drilled and get as much turnover ball as they did, they are formidable," said 34-year-old World Cup winner Catt, who could conceivably have made his last Test appearance.
"It is disappointing to lose the way we did, but it is even more disappointing the way we created chances but couldn't finish them off to keep us in the game.
"We've only had two weeks together, but there are no excuses. We had a couple of opportunities we could have taken that perhaps might not have changed the game, but definitely put us up there with a shout.
"We had a lot of possession again (63 per cent), and turned the ball over. Against a side like Australia, you cannot afford to do that.
"It's not nice. When you lose by 30 to 40 points, it is very hard for the youngsters to come in and develop because they feel as gutted as you do. There is not that stepping stone you desperately need for youngsters to get to international level."
Catt, though, has urged patience while boss Andy Robinson's new coaching support staff of Brian Ashton, John Wells and Mike Ford settle into their roles after a tough baptism Down Under.
"What we need to do is maintain what we are doing," Catt added. "It is the first time we've had the new coaches on board, and it is going to take time.
"What you hope for is a lot more than three or four players coming through, and I think that is the disappointing thing.
"It was just the basic stuff - catching, passing at the right time - and we got the basics wrong, it is as dead simple as that. We were hammered."