The Bundesliga side are still searching for their first win in Group H following a 1-1 draw in Cyprus that leaves Dortmund still six points behind titleholders Real Madrid and Tottenham in the standings.
Sokratis Papastathopoulos' towering header cancelled out an opening goal from Mickael Pote that was gift-wrapped by Dortmund goalkeeper Roman Burki, who compounded a stray pass by spilling a shot from Lorenzo Ebecilio straight into the scorer's path.
Pierre-Emerick Aubameyang had a wonderful chance to win the game at the death, only for the forward to see his close-range header kept out by a combination of substitute keeper Raul Gudino's body and a post.
"The result is disappointing. We started well, but did not go on. Then we played more slowly and worse," Bosz told UEFA.com.
"We have to look at ourselves. We did not get the ball forward quickly enough, we tried to improve that but did not manage to do so.
"In such a game it is important to score the first goal. We had the chances in the first half, but failed to do so.
"The result in Madrid was not good for us. We know it's difficult now, but we will have to win the home game against APOEL and then see what the two last matches bring."
Bosz was also quick to defend Burki, who came in for criticism earlier in the European campaign after conceding twice at his near post in the 3-1 defeat to Tottenham at Wembley.
"Roman has often helped the team this season," he added.
"This happens in football, he has to carry on. The team will not blame him."
Dortmund - who saw defender Omer Toprak forced off in the second half through injury - now go on the road for their next three matches before hosting APOEL in a must-win European fixture on November 1.