Could I make sure that there was nothing left out?
I bought some things at your store the other day, and I think there was something that was left out, so I just wanted to make sure before going back to your store.
(something) forgotten, left out
入れ忘れ
That there was nothing left out
商品の入れ忘れがなかったか
Could I make sure that～
～認してもらえますか
電話の間に合わせをするとき、I bought some things at your store the other day, and I think there was something that was left out, so I just wanted to make sure before going back to your store. という聞き方を使っていいと思います。
ご参考になれば幸いです！
アメリカ合衆国 
