After copying the template you must change the POM fil so it reflects your project. Specifically you must changes the following lines:
<groupId>com.stegger</groupId>
<artifactId>Javafx_FXML_template</artifactId>
Update the tags to represent your project.
Once you open the project in NetBeans you might also want to change the project name etc. But the project should be ready to run from the start. If you experience any issues running the project you might want to edit the etc/netbeans.conf file under the NetBeans installation folder and setting the netbeans_jdkhome property:
netbeans_jdkhome=/path/to/jdk-12
Save and restart NetBeans.
The project is set up using the guide from OpenJFX found here: https://openjfx.io/openjfx-docs/#IDE-NetBeans