You can download a CSV export of your Stories analytics under the PRO, ELITE, ADVANCED, MASTER, CORPORATE, ENTERPRISE and AGENCY plans!
See Reach, Impressions, Exit Rate, Completion Rate and more in this handy Stories-only report.
You will be able to export this data in the Overview section of your main menu. Adjust the date picker in the top right to your desired time period. Then just click on the grey download arrow at the right hand side of the 'Most Recent Stories' box!