The Royal Blues suffered a 3-2 home defeat to Galatasaray in the second leg of their last-16 tie on Tuesday to bow out of the competition 4-3 on aggregate.
"We played really well in the second half, we had chances, but it wasn't enough," he told UEFA.com. "It's a shame as we had a great chance to go through. It's sad, but we have to get our heads up and even if it's not easy to cope with all of that, I think we now have to focus on the league.
"Schalke have experience of playing big matches, and there are many players here who have that experience too. Sometimes when you really want to do things right, you really want to do everything to qualify, then you lose concentration.
"It's the whole squad's fault if we didn't go through. You have to congratulate Galatasaray for going through. We have to look at what we've done wrong during this game and make sure we don't repeat those mistakes in our upcoming league games."
Schalke are currently fourth in the Bundesliga.