I don't have LV on this machine so I can't look at your code. If you want the graph to show (0,0) as being in the center you need to shut autoscaling off. Using the Graph properties page select the Scales tab and shut off the autoscale for both scales. Enter appropriate values for the scales e.g. -5 to 5. This will put (0,0) in the middle of the graph.
Hope this helps.
Now Using LabVIEW 2019SP1 and TestStand 2019