I think you made a mistake on the number of his absences. Could you please check that?
この場合、次のような言い方ができますよ。
ーI think you made a mistake on the number of his absences. Could you please check that?
「彼の欠席日数が間違っていると思うので、確認していただけますか?」
number of one's absences で「欠席日数」
ご参考まで!