You forgot to

#. You forgot to ~

~을 깜빡하셨군요.

 

You forgot to lock the door. 

You forgot to give me back my bicycle. 내 자전거 돌려주는 걸 깜빡했구나.

You forgot to flush the toilet again !  변기에 물 내리는 거 깜빡했구나.

You forgot to sign your name.

You forgot to turn off the TV again.