Do not remove the Page to Blog macro that is part of the template and is loaded into the new page when it is created. When you save the new announcement, this macro will convert the page to a blog post, and add it to the list of Product Announcements on this page.
If you do accidentally remove the macro and save the page, it will be added as a child under Product Announcements, instead of a blog post listed on this page. In that case, view the page, and in the ... menu in the upper right corner, select Convert Page to Blog. The page will be converted to a blog post, with the creation date of the page used as as the publication date of the blog post.