I didn't say that Atalanta has qualified for next season's UEFA Champions League; what I said was that the win Atalanta had against Lecce has given them hope of qualifying for next season's UEFA Champions League because Juventus is leading them by one point and there are two remaining matches for the Serie A season to end. For a long time, Juventus has been struggling to win their matches in the Serie A, which has put them in this condition, and if they continue with such performances, Atalanta might overtake them in the Serie A table. Juventus next match is against Bologna, and they might likely drop points against Bologna, which will give Atalanta an advantage to enter the top four of the Serie A table if they win their match in Serie A.
I think Atalanta will definitely qualify for the UEFA Champions League next season, now they are ranked 5th and for this season there are 5 teams that qualify from Serie A and also Atalnta is 6 points ahead of Roma who is ranked 6th so there is no possibility again for Roma to be able to catch Atalanta.
As for the competition for UEFA Champions League tickets for next season, I think everything is over, there are 5 teams that have confirmed getting these tickets, namely Inter MIlan, AC Milan, Bologna, Juventus and Atalanta.