You could fix your axes to start at Q1-18 and end at Q3-18, but that would mean it won't work when new dates come along. For other potential solutions, we'd probably need to see a packaged workbook.
You are right, but as the data grow this will also increase. Do you think something else can be done, because this margin just makes the whole chart look a bit incomplete.
Any chance you could share a packaged workbook?