ㄴ 거 맞다

that's what happened, right?

Confirms something already done or already true. Politely, it is the front-desk check: 한 객실 필요하신 거 맞으시죠? 'you need just the one room, correct?', 다 가져온 거 맞아요? 10개 맞아요? Between friends it fishes for agreement — [호들갑 나 연기 잘한 거 맞지?] 'my acting was good, right?' — and sharpened it becomes a challenge: 당신들 입단속 제대로 한 거 맞아? 는 거 맞다 is the same check about something ongoing.