Rudi Garcia said Roma's lack of recent Champions League experience was the difference in his side's 2-0 defeat to Manchester City on Wednesday.
Roma returned to Europe's top club competition this season after a three-year absence, whereas their opponents are playing in their fourth straight tournament.
Samir Nasri's opening strike went in off the post, but Kostas Manolas' header bounced off the woodwork, and Garcia said Roma were unlucky not to score in the opening stages.
"In the first 15 minutes we could have done more and scored," Roma coach Rudi Garcia said. "But we were also unlucky. They hit the post and the ball went in. We hit the post and it bounced out.
"Manchester City have more experience and maturity at this level, whereas we are learning and need to improve some elements. We also need some even stronger players if we are to reach teams of that level.
"We should've made more of our opening half-hour, when we had City on the ropes. Similarly, you can't allow a player like Nasri to shoot undisturbed from distance."
Garcia insisted that if a few bounces had gone the other way, Roma could have competed with Manchester City until the end.
"This was a final, we knew even without some players that City were strong and they proved it," the coach said.
"It was a very balanced game and you need luck too, so tonight fortune chose its team with those two uprights. I do think we could've scored and done something more in this game."
Garcia said he will use the experience of playing one of Europe's best clubs as something to learn from.
"They are not the Premier League holders for nothing. I am really disappointed for the lads, as it was possible to do better and qualify, but it shows us the steps we still need to climb in order to be among Europe's top clubs."
Roma did advance to the Europa League, but Garcia said it will be secondary to their Serie A campaign.
"If we want to play the Champions League again, then we need a great Serie A campaign and be ready for Sunday. That's what I expect from my players, I'll try to get this disappointment out of their heads.
"We have the Europa League now, which is an international tournament, but the League remains our main objective."