What type of ad are you running? It’s generally harder to get impressions on a socially recommended ad (so a page post ad or page ad that includes stories about their friends liking it); if you have it socially recommended, try removing that and see if you get more impressions.
Try this: start a new campaign with an identical ad. Facebook Ads doesn’t show an ad to all 155,000 users at once. Your targeted users have to log into Facebook to view the ad. So it will take time to reach all users. You can try raising your bid even higher for a few days; that might get you more impression share. Put it at $1.25 and let it run on a $30 per day budget. A higher bid, even beyond the actual cost, can increase impressions by quite a bit. Facebook Ads wants to see how high of a CTR your ad is going to get, so it will deliver a high amount of impressions until it has an estimate. If your ad doesn’t get a high CTR, Facebook drops your impressions in favor of an ad that does. The higher the CTR of an ad, the more Facebook makes per impression.