The Samurai Blue star had two big chances to score in the extra-time DFB-Pokal semi-final win over Greuther Furth and lamented failing to do so
The victory sees BVB progress to the decider where they'll face either Bayern Munich or Borussia Monchengladbach, who pface off on Wednesday.
However, Kagawa told reporters his team-mates would need to convert their chances in front of goal in coming weeks, after waiting until the final moments for Ilkay Gundogan to clinch their spot in the final.
"I felt like we could create chances, and just like [Saturday's match against Bremen] our inability to convert those chances is something for us to consider," Kagawa said.
He added that Greuther Furth were never going to be easybeats considering their form in the 2.Bundesliga.
"They're leading the second division, so it's a mistake to think that they'd make it easy for us. They were also playing at home so they played hard," he said.
Kagawa added he felt his side's failure in front of goal was a mental problem, rather than a technical one.
"We certainly made mistakes. I made several mistakes in the second half. And in that context we need to improve our focus, because those were casual misses," he said.
"But I think somehow we'll be able to figure it out, because it's not a problem with our technique. I think if we work on improving our concentration, and in that sort of situation we can treat the ball better when we have possession, [we'll be fine]."
The Japanese also had two big chances to get his name on the scoresheet and lamented the earlier when his first-half header from six yards out sailed over the bar.
"The header in the first half is absolutely something I needed to convert, and it's something I have to think hard about," Kagawa said.
"The shot in the second half off my left foot was a bit of a difficult one, so I didn't think it would go in unless the goalkeeper deflected it. But regardless, I still have to convert when I have the opportunity."