Hello Gavin Jeffers,
Thank you for adding a packaged workbook to this post. Is the desire to just push out the view to 2/1/2015? I wouldn't think so since it looks like you already have done this by using the Report Date Parameter with a Reference line in the view.
Is the desire to extend the Burndown and Target lines and/or the Trend line?
Updated view with parameter to control end date is attached just in case this is what is desired.
burndown_pv.twbx 59.5 KB