Ads to specific categories being repeated

Hi there, I have Simple Ads Manager Version 2.9.7.123. (I did try and upgrade to SAM pro but had issues)
Anyway what I have done is created Ads places and in that put loads of different ads.
Then I want certain ads only showing in certain post categories so I have gone to the Edit advertisement page and then extended restrictions and clicked “Show ad only in single posts or categories archives of certain categories:” then I have selected the post category I want to display the ad in.
This seems to work however on some pages I seem to get the same ad being repeated a number of times as I have 20 ads on each category page but maybe not enough ads to fill these places? Is there anyway to not show repeats?

https://wordpress.org/plugins/simple-ads-manager/