Hi,
Edit your menu item via the Joomla menu manager and make sure that the "sub elements filter" setting, under the "products options" tab, is set to "direct sub elements". If it's set to "all sub elements", you'll get the products linked to the sub categories below the sub categories listing.
If that is already the case and you still see some products below the sub categories listing, it's probably because you directly linked these products to the current category of the page. So in that case, you need to check the "categories" option of these products so that the products are only linked to the sub categories and not the main category.