Why does it say 'Layout canvas' above the paragraph?

You have the Layout canvas field label set to be visible.

There's a field label above your paragraph because Drupal adds this by default when you add a field to an entity.

To remove this label, navigate to Structure > Content types > Basic page > Manage display.

Then in the Label column, click on the drop-down next to Layout canvas and select 'Hidden'. The label will now be removed from your template and page.