Formatting grouped horizontal axis of Pivot Chart

Hi, I've got time-based data and I'm using a PivotTable to smooth data collected daily by grouping by in 7 day intervals and taking an average. I've plotted the smoothed data, but the axis shows each of the 7-day periods instead of the year as I would like (see "Problem Outline" attachment). I have tried to apply custom number formatting, but this appears to be ineffective (see "Ineffective Number Formatting" attachment). I've attached the actual spreadsheet in case it's of any help. I'm using Excel 2010.

Thanks.