I also noticed that it seemed to be ignoring options, however it turned out that I simply had a very old version of Gnuplot installed to /usr/lib64/perl5 that was taking precidence in my perl path. Moving that installation of Chart::Graph aside enabled these options to work.
The recent review of this module reminded me of the fact that the Chart::Graph::Gnuplot module is severely broken.
Some time ago, I started using it on an old debian/woody box. It worked as advertised. But then, in the transition from gnuplot 3.7 to gnuplot 4.0, (which most likely occurred in a woody->sarge dist upgrade) the module just stopped producing any meaningful output. I sent mail to the authors and created an RT ticket: rt.cpan.org/Ticket/Display.html?id=14757
I offered to fix the problem and upload a new distribution to CPAN. I have never received an answer.
The problem is really an incompatible change in gnuplot. The transition from 4.0 to the current development version will bring the same problems again, even if the current problem will be fixed. And then, one would have to keep the old interface for users with the old gnuplot binaries...
Ergo, you shouldn't use this module in version 2.0 or earlier (which is all that's availlable right now). If it works for you, it is unlikely to keep working in the future!
The documentation and code aren't consistent. In the Gnuplot module, the documentation states that you can specify (for example) "extra_opts" as extra options. If you actually use this, though, the module prints an error message and ignores the options.
I worked around this by specifying:
"y-axis label" => 'y-axis"\n<code to run>\n<code to run>\n#"'
This works fine but is a dirty hack. I hope the author fixes this.