Die Roten lost the first leg 2-1 at home on Wednesday. Arturo Vidal put the hosts in front, but two goals from Cristiano Ronaldo secured the win for Los Merengues.
Vidal had a chance to make it 2-0 to Bayern, but he missed his penalty, giving the visitors their chance to fight back for a win.
"We had no luck tonight and it was the small details which made the difference," Ancelotti said, according to ESPN FC.
"[Arturo Vidal] missed the penalty when we could have made it 2-0, then we conceded right at the start of the second half and that changed the match.
"Sometimes you miss a penalty, that was not the first one, and it will not be the last one, but we can build on the first half.
"It will be more difficult in Madrid, but we still have a chance, we are still alive. We will look to take our chance. We will try to do our best."