Is this sentence correct?

Question:

クッキーが三個もいなかった

I'm trying to say "I only had three cookies." at first I said クッキーが三個しかいった but my Japanese teacher said it wasn't necessary

Answer:

this is the correct sentence.
クッキーが三個しかなかった。
クッキーが三個　the counting is correct.
クッキーが三個も- this applies either you see three cookies you were not expecting them to be left that many, or, you see there are not more than three left. depending on if the clause is followed by affirtive, or negative form.
いる、いない- applies to the existance of people, animals.
ある、ない　- it applies to existance of object, things.