The 30-year-old all-rounder bemoans missing out on the "huge opportunity" to beat the 2007 champions in their own backyard, reports bdnews24.com.
Mahmudullah, who led the Prime Bank to Dhaka Premier League title last season, will play for Sheikh Jamal Dhanmondi Club this year. He is the first player to have been selected in the players draft.
He started training from Tuesday on his return from vacation.
The time away from the field might have been refreshing for Mahmudullah, but the pain of the March 23 match was far from erased from his mind.
On the brink of elimination after two successive defeats in the Super 10s of the World T20, Bangladesh had needed just two runs from the last three balls to seal victory at the M. Chinnaswamy Stadium in Bengaluru.
With the experienced Mahmudullah and Mushfiqur Rahim at the crease, the upset seemed all but pulled off.
But a brain freeze saw them lose three wickets in the remaining deliveries as Bangladesh fell one run short to plunge their fans into a state of shock and utter disbelief.
"How can I forget that? When Mushfiq and I were batting never thought that we could lose," Mahmudullah said on Tuesday.
"Actually Mushfiq's wicket after two fine boundaries was unthinkable. After that, my dismissal was unimaginable as well - it was such a mistake."
Both the batsmen targeted the leg side for big shots off Hardik Pandya but ended holding out to midwicket.
"The ball was there to be hit for sixes but I missed. But I can't go back and fix it. In the future, I will try to choose safer options in such situations," Mahmudullah said.
A single after that could have taken the match to a Super Over but a run out, due to the quick wits of India skipper Mahendra Singh Dhoni, prevented that.
"There was still hope but it didn't happen, it's actually my fault. I made a senseless mistake and was responsible for the defeat."
"I just want to say - I apologise to everyone. I am yet to say officially something after that match ... I will try to handle such situation smartly in the future."