My chart's X-axis isn't working properly
 

Hi:

I've started a simple line chart that's based on 4 columns and (right now) 5 rows of data.

I'm tracking my blood pressure so the column headings are Date, Systolic, Diastolic and HR.

The idea was that I would take my blood pressure once a week, on the same day every week, but I haven't been that religious about doing so; I've been a day plus or minus 7 days twice and also missed a couple of weeks along the way.

The numbers are appearing in the graph properly. However the graph's X-axis has ticks for every seven days (8/29, 9/5, 9/12, etc.) even though I don't have a perfect "every 7 days" track record in recording.

What am I doing wrong here?