I do not seem to have your white border behavior with a simple example I just tried:
Can you try if with this simple plot you also have no whitespace on the left of the plot (so it depends on your specific plot data) or if you still have it and then it may be due to a difference in Pluto or Plots version?
For reference I am using latest Plots (1.25.0) and latest Pluto (0.17.3)