"お待たせ！教科書取りに行ってた"
- Thanks for waiting! (待っててくれてありがとう) I went to go get my textbook.
- Sorry to keep you waiting! （待たせてごめん）I had to get my textbook.
短く・とてもカジュアル（上のほうは少しポライトな感じ）
- Sorry to keep you. I went to get my textbook.
- Hey, sorry. I was getting my textbook.
- Sorry, I was getting my textbook. Let's go. (ごめん、教科書取りに行ってた。行こう）
・Sorry to keep you waiting. I went to grab my textbook.
・Sorry to keep you waiting. I went to grab my textbook.
「お待たせ！教科書取りに行ってた。」
Sorry to keep you waiting が「お待たせ」、
went to grab が「取りに行ってた」を軽く自然に言えます。
・Sorry I’m late, I just went to get my textbook.
「遅れてごめん。教科書取りに行ってただけ。」
アメリカ合衆国 
