As a general comment, it's most often a bad idea to use the chat's internal data table, mainly because it can't grow. It's easier to display a subreport below the chart to show the data, based on a similar query. However, you should be able to reduce the size of the char area in design mode and save that, and it is possible to manipulate the chart through code, but that can be a bit tricky.
(°v°)