I'm terribly sorry but due to an urgent matter, I must leave right now at the beginning of the lesson.
"今始まったばかりなのにお暇しなくちゃいけなくてすみません"
I'm terribly sorry but due to an urgent matter, I must leave right now at the beginning of the lesson.
本当にごめんなさい I'm terribly sorry
急用で、due to an urgent matter
～しなければならない must ~
すぐに right now
レッスンの初めに、at the beginning of the lesson
日本 
