To add on Francis suggestion:
the labels will not appear in your exported file if you don't select them to be visisble. The general principle is: the appearance of your graph in the preview panel is largely independent from what you see in the overview panel.
For example, you see labels in the overview panel, but if you don't select "Labels visible" again in the preview mode, the labels won't show up. So do select this.
And as Francis said, click "refresh" in the preview mode, and again to see the effect of each parameter you changed!
Hope it helps,