Are you checking your list to make sure you didn't forget to buy something?
Are you double checking to make sure you didn't forget anyone?
この場合、次のような言い方ができますよ。
ーAre you checking your list to make sure you didn't forget to buy something?
「買い忘れがないようリストを確認しているの?」
ーAre you double checking to make sure you didn't forget anyone?
「買い忘れた人がいないよう再確認しているの?」
ご参考まで!