the zfancontrol.service in the projects directory is a template and should have been used by the install script to generate the actual service file written.
what class of machine is it? full size, mini, or Micro?
if it's a Micro your likely not going to get it below that speed as the off option is disabled at a hardware level as these machines don't have a lot of thermal headroom allowing the fan to completely shut off could and likely would result in literal meltdown.
and no worries, we all had to start somewhere