Hi Jelena - I don't believe that method for setting up Plone on Windows tries to set up Plone as a Windows service. It's true, the old Plone 4 and 3 installers for Windows did.
When you run
bin/instance start does Plone run correctly? ie. can you browse to http://localhost:8080 successfully? If so, you can ignore the warning about not being installed as a Windows service.
I'm rusty with Windows, but to have Plone run when Windows reboots, could you set up a .bat file, e.g. plone.bat, containing something like this:
and place that plone.bat file in a general startup folder that Windows reads at boot time?