Best advice is to contact Appnitro through a support ticket. they can restore the 'count' of domains you have left if you uninstall Machform from a site.
In the past I've had the same thing happen and they happily restore the number I had left on removal of Machform from one of my sites.
It would be nice to have in your members area a real-time monitor of the sites it's installed on, or removed from but currently the monitoring system is internal to Appnitro.
Also I'm not sure if it regards "localhost" (your own PC with a webserver running) as a "domain" or not if it is a test environment and not live on the web.
