The Croat said his side "absolutely" changed in the second-half by executing the passes from the sides as the channels started opening up.
"But we were not aggressive enough. Many more things we need to work on," Stimac rued.
With less than two minutes of regulation time left, it was Adil Khan, who came up with the equaliser, as he glanced his header past the near post, and into the back of the net.
"We deserved to win this game. We pushed until the end and created enough chances to win the game. But our scoring was not good enough," Stimac said.
No blame game
In their previous game, India fought valiantly to hold AFC Asian Cup 2019 champions and FIFA 2022 World Cup hosts Qatar to a goalless draw in a match Sandhu made 11 saves. Stimac, however, refused to blame any player.
"Sometimes you've a great day, sometime you make mistakes in making judgment. We aren't here blaming anyone. I defend my players with my heart," he added.
India played in front of 65,000 fans at the Saltlake Stadium and the Croatian World Cupper said he would remember this forever.
"This was amazing day for indian football, many of them will never forget the ambience, the support they received in Kolkata. I had many big names in my career. I'll remember this as as one of the biggest ones," the 52-year-old said.