맞추다 is making things line up with each other. Two combinations run through these lines: 끼워 맞추다, jamming pieces together until they fit, used four times here for forcing a story or an excuse to add up (너무 억지로 끼워 맞춘 것 같은데?), and 알아 맞추다 / 때려 맞추다, landing on the right answer — that is, guessing (총 몇 박스 파는지 알아 맞춰봐요). Note the spelling: for 'guess correctly' the standard verb is 맞히다, but subtitles almost always write 맞추다.