Upvote:4
Unless you have a stamp like this (provided by Photographers Direct):
Which has a date by which you have to leave the country and it's within 1 week of the date of your entry, you are allowed to remain in the country for the full 90 days that are permitted for you by the US Visa Waiver Program. So if you're planning to leave within 90 days it should not be an issue without having to notify anyone.