Like all elements of Pinterest, story pins are in flux. I have created some that get 50,000 impressions and some that get, like yours, 200 impressions.
Impressions can very based on times of day, subject matter/content, and boards to which you pin them. By trying different variables until you find a combination that works, then continue with that combination.
It seems as though Pinterest have shifted to giving priority to paid advertising over free impressions. Some users have found they regained their audiences by spending as little as $5 a day.