Don't worry! There's nothing wrong with the template.
Minimal blog template might look broken at first when there aren't any blog posts published (When the blog is empty) This is the expected behavior. This happens because of the way the 'Subscribe' module is designed. The template requires at least two blog posts/articles published in order to display the 'Subscribe' module perfectly.
Once you published two blog posts/articles, the template will look exactly like the preview.
See the screenshot below for further clarification.