Yes you should tell them, regardless of the context you have an incorrect piece of inforation in the policy which will make it void.
Do it on the phone and they will tell you there and then whether there is a little more to be added to the premium. Its unlikely to be much if its only contents insurance, but you can discuss it with them and if necessary demand to speak to a Manager to complain that this question wasn't asked of you on the internet application.
Good luck.



