In order for the markup created in the editor to replace your default markup the URI needs to be that of the URL of your webpage. This is because the URI is how Schema App knows where to deploy your code. You can check this by opening the data item and looking at the URI. 

Note: it is important to copy+paste the URL completely so as to not miss any trailing slashes. 

If you need assistance in changing the URI, you can find steps here

In the event that everything is setup properly and the markup is not deploying please reach out to and we will be able to troubleshoot further.