Markus Schopp rued missed early chances and said a penalty shoot-out loss was the 'worst way' to exit the EFL Cup.
The Reds lost 5-4 in the shoot-out at League One Bolton Wanderers in the first round on Tuesday, with Devante Cole missing the decisive spot-kick.
Before his post-match press conference was cancelled by a fire alarm, Schopp told the Chronicle: "It's the worst way to go out with the last penalty. We did a good job for 60 minutes but we have had a problem in pre-season and in Cardiff that we create a lot but don't score. We have the big opportunity at the start with Vic's header (Victor Adeboyejo). To open a game in this way would be awesome, so we have to improve that. After 60 minutes, it was not anymore our game. But we made changes which caused this."
Defender Jasper Moon added: "It's disappointing to go out but we can take some positives. A lot of lads got minutes who wouldn't normally play. But overall we are disappointed that we lost.
"The style of play the new gaffer has come in with is trying to play out more, and in the first half we got it going. In the second half they stepped higher and pressed more which made it harder for us. They played higher so balls in behind would have been the option but they made it hard for us."
Cole missed the decisive penalty on his first game back for Barnsley after a 2014 loan spell. Moon said: "He's going to be disappointed, all the lads are but we just have to hold our heads high and prepare for Saturday now.
"Not many of us have played in the cup before or in a shoot-out. It's a good experience, but to lose on penalties is obviously sad."