If you have set up Timeshift (which is one on the list of "things to do after installing Zorin), try going back to a time either before you installed Pano, or failing that, before you uninstalled it and do it properly, using the same method you used to install it in the first place, e.g. go to the Software Store, click "installed" and locate Pano, then click on uninstall.
Alternatively, @Aravisian posted a very useful guide here (scroll down until you see the instructions about how to UNINSTALL using APT in the terminal): Common Terminal Commands
Using Timeshift was the answer for me when I messed up installing, then uninstalling something.