You were right and Barcelona drew with Atalanta, but Barcelona tried and played great, but Atalanta played one of their best games in a while and Ederson's goal was just great, real soccer art.
I think if Szczesny had played better and not missed the ball between his legs, Barcelona could have won, but they still helped Real not to go out, which means that at least there was no contractual game here and everyone played to their full potential.
Barcelona played without any burden in this match, because even if they get any result, their position is really safe to be in the last 16. Atalanta who had to accept the fact that they had to be in the play-off round after failing to get a win in this match. Yes, the draw they got only made them in 9th position, only one rank below the safe position to be in the last 16.
They worked hard, but their hard work was not enough to make them safe because the opponents they faced were also not that easy to beat.
Barcelona tried their best in this match, though Atalanta did well too, and they tried their best to see that they win the match, but unfortunately it ended in a draw. I think this could be a very good result for them if they win the match, although the result did not affect Barcelona since their position in the table is still okay. But Atalanta were trying their best to see that they win so they will qualify. But you are right; they can still do better in the coming round. Since they are not a weak team.