The Bees were beaten 2-0 at Anfield on Sunday.
Flekken said, "It was a tough game. I think we did well in the first half. We had to find our way in the first 15 minutes but we found our rhythm and then we should have done better on the transition when we conceded. It seemed like they stepped their game up in the second half and from their second goal it was like a finished game.
"With the offensive forwards they have you know it is a tough match every time you come here. You prepare yourself to stop as much as possible. I saved some, didn't save enough, lost the game.
"There are a lot of positive things. We had some good moments with the ball, maybe we should do better at finding that link up to our forwards. That is something to analyse. We have a game on Wednesday so we have a chance to win."