ok, it seems what you want is for the xaxis ticks labels and alls going through the midline of the plot.
ggplot doesnt give elegant ways to do this at present.
There are a bunch of proposals at : https://stackoverflow.com/questions/17753101/center-x-and-y-axis-with-ggplot2
I would probably try https://stackoverflow.com/a/49202967/11726436