So I have an issue with the iStripper app is that it begins for seemingly no reason begin to download previews for girls and use that in the show instead of using the ones i already own.

Is there a way i can make the app play ONLY the ones i bought and not download any new preview girls unless I click the download/buy button for them?

Go to the Settings page of the app (the cog-wheel icon in the title bar)
Enable "Adanced Settings"
Scroll down to the "Clips" section
Set "Free Preview Push" to "Never"

For some reason it's locked to 10 mins, no way for me to change it.

Bronze / Free level can not change it.
Since you have not Purchased any cards ( Only Free card with Free Credits )
you will not be able to change it.

Want to change it,
Purchase some credits and purchase some cards.

Is there a way i can make the app play ONLY the ones i bought

Yes - but you have to actually buy some first, not just download previews.