I have NEVER once itemized my stuff although I rarely bring back anything of significance. I just write $20 on the front of the form as a catchall for anything I may have and never write anything on the back. I leave it completely blank. Even on being secondaried a number of times where I had cigarettes and alcohol but nothing over the limit and nothing itemized, they have never said a word about it so I assume it is fine and whether it is technically correct or not, I've done it that way on over a hundred international arrivals and never had an issue so I will continue to do unless it creates an issue. I'd say the OP just got a wannabe bossy Customs agent and even then nothing came of it so I wouldn't worry about it or change anything myself.