The French side beat fancied England team Saracens and will meet Exeter in their semifinal on April 30 in Bordeaux. Exeter qualified after a 42-17 thumping of the South African side, the Stormers.
Kerr-Barlow told Midi Olympique, "It wasn't perfect, but we are very happy to be in the semifinals. I don't know if we were favourites. We knew we had to improve, and the team showed their quality.
"We expected a strong performance, especially in the playoffs against a team like Saracens. They are always strong in the rucks. We didn't dominate in that area but we found a way around that."
Kerr-Barlow said his first-half try resulted from a move he and No8 Gregory Alldritt put together during their week of preparation.
"When he called it, I struggled as we had just completed more than 10 rucks. I thought he was going to kill me but, fortunately, I found the space and managed to score."
The side's preparation had not been as good as wanted, and they would have to lift themselves against Exeter.
"We were a bit light on support. But we are happy. With this club it is always the goal to try to play to the best of our abilities. Sometimes we are not 100 per cent but, like last week, we found a solution. We don't think too much about the future, we build."
It is the third consecutive season La Rochelle has reached the semifinals, but the first time the club has played against Saracens.
"They have a huge squad, with lots of experience and lots of Test players. We knew it would be a big game for us. They put a lot of pressure on us in our 22m. Fortunately, with our defence, especially Fijian forward Levani Botia, we found the solutions. The team spirit was huge today. Sometimes it's not the talent that counts. However, we still haven't finished the job."
Before their semifinal, La Rochelle has two rounds of the Top 14 to play, with a semifinal place also beckoning. La Rochelle is in second place, six points behind Toulouse, who also qualified for the Champions Cup semis, where they will play Leinster in Dublin.