Town once again went with a development squad side for the 1-0 third round replay defeat, while the U’s picked a vastly more experienced team.
Although the result means Town can now focus fully on the league, with United facing further fixture congestion, Harris denied that had come into their thinking.
He said: “I can be really serious, if we could have won, we would have done.
“We’d have gone and played on February 1 at Eastleigh as we wanted this FA Trophy journey to continue.
“I said to the guys, they don’t get many opportunities to play at Wembley in their career. So don’t pass it over and I don’t think they passed it over, I thought they did ever so well.
“We just wanted to win the game if we could, but if we didn’t, get something out of the game and I think we did.”
Town could indeed take plenty from the match too, with 16-year-old Luke Trotman making an assured debut at right-back.
Youngsters Brett Longden and Ian Rees both impressed too, as did striker Zane Banton who came off the bench in the second half.
On Trotman, Harris continued: “He got off to a great start, went down the line and put a fantastic cross in the first five minutes, which settled him down a bit.
“We played Reading last week in a squad game and he was superb then.
“As John (Still) has always said, it doesn’t matter how old they are, if they’re good enough they’ll go in.
“Luke went in and looked very, very comfortable.”
Longden, who had undergone a tough examination on Saturday, was switched to left-back, but was the star performer as Harris said: “Anybody will tell you it’s difficult for a right footer playing left-back.
“We said to him, sometimes just take a swing with your left foot and he did.
“He tried to do it right every time, and I thought he was absolutely fantastic.”
Rees and Banton also showcased their talents, with Harris saying: “Ian Rees in the middle of the park, he’s up against (Tom) Champion and (Luke) Berry, two very, very good players.
“I thought he did exceptionally well. Zane came on and nearly nicked a goal, so the future’s bright, the future’s orange.”
The only frustration aspect on the night for Harris was the manner in which Hatters conceded as Ashley Chambers was allowed too much space to shoot, with the ball taking a huge deflection off Ryan Inniss.
Harris added: “The one disappointment was the goal really because it was from a throw in, we should have marked better, but we never, we didn’t pick up and they got a deflected goal.
“In the second half, Elliot (Justham) was fairly redundant. Did we look like scoring? Not really, we had the offside goal, but the linesman put his flag up straight away, so that was disappointinh.
“But against a very strong Cambridge side, we have to be delighted.”
For all the latest Luton Town FC news, reports, stats, player profiles, live match updates, MOM poll, prediction table and a complete fixture list, visit our Hatters Microsite.