The watermark is still on my plugin or it's showing unregistered.

Download the latest version of FxFactory:

After installing, launch the FxFactory application and sign in with the same email you used during purchase. You may need to create a new password if you have not done so already. Once you login successfully, all the products you purchased will appear inside the app.

After you have licensed the plugins, restart Final Cut Pro X and check if the watermarks are still there.

In Final Cut Pro X you may have to change one of the parameters of the plugin, forcing a change and re-render the clip.