The La Liga giants were fortunate to progress to the last four after a 2-0 loss at Borussia Dortmund on Tuesday saw them edge through with a 3-2 aggregate victory.
But it could have been worse for Real after the Bundesliga outfit missed several chances to claim an even bigger win on the night.
Ramos said he and his team-mates needed to think about their performance despite being delighted to be in the last four.
"Obviously it was not a good first half for us," the defender told reporters.
"We're delighted to have made the semi-finals, but we have to reflect on this performance.
"The first half wasn't so good but we were better in the second.
"We're not worried about who we play now. To win the Champions League you have to beat the best."
Ramos said he was unfazed by who Real draw for the semi-finals, and praised coach Carlo Ancelotti for helping his side hang on against Dortmund.
"The coach is there for that, to tell us what he needs to and if we go back out (for the second half) maybe we won't be going through to the semi-finals," he said.
"We need to be happy because it's not easy to do - four consecutive semi-finals. Now we need to see who we get."
