@Realize make sure you exclude some url's like checkout, account etc 

You could also create a segment for those recent purchasers, just realize that segments are not updated realtime so there might be some delays.

Also make sure that if people close down the popup they don't keep re-appearing to them for a specific time period.

In short play around with the options, check where the issues arrises (see if you can replicate the problem) and adjust exclusions

@Realize agree with @Omar here - when setting up your form, make sure to exclude its appearance on specific landing pages from your store so that users don’t trigger the form on that page. If you have screenshots to share of the setup of your form, feel free to pass it along. Agree that it’s best to see how you might be able to replicate the issue in an incognito window to see where the form might be showing for users so that you can troubleshoot it. 

Thanks! 
-Cass.