When you add to the JFrame the default location is CENTER but since you add to the chart to the PAGE_START now its not scalable...
solution:
take it out and just say
frame.add(chartPanel);
and for the errorPanel and ButtonPanel
just make a new JPanel with BorderLayout and add it to the SOUTH of your Frame Layout. Then inside that JPanel add your ButtonPanel and ErroPanel just like what you did in your Jframe..