The European champions missed out on automatic qualification to the Mundial following a 0-0 draw with Northern Ireland in their final group game on Monday.
Switzerland duly took advantage to top Group C after dispatching Bulgaria 4-0 to book their place in Qatar and consign Italy to the play-offs, which will take place in March next year.
“We can’t do anything about it now, we have this game in March and will try to give our best,” Mancini told RAI Sport, referring to the play-offs.
“At the moment, we are struggling to score goals, despite dominating possession and the initiative. Northern Ireland put everyone in defence and we struggle to break sides like that down.
“It’s a pity, because we should’ve sealed the group long before it came to this. We just need to rediscover what characterised us up until today. We had two missed penalties in the decisive matches, so that shows we had the chances to win.”
“Now we prepare for March and we go into the play-offs confident. We’ll book our place in the World Cup in March and hopefully win the tournament too.”
Italy missed out on qualification to the 2018 World Cup in Russia after losing their play-off to Sweden.