touch id a payment for an app said it free for three days was an accident how do i fix it or can i just delete the app and it wont charge?

Deleting an app won't cancel its purchase nor any subscription that you've taken out in it. If it is a subscription : View, change, or cancel your subscriptions - Apple Support

If you are looking for a refund then purchases are considered final, but you could try the 'report a problem' page to contact iTunes Support and see if they will refund or credit you as a one-off : http://reportaproblem.apple.com

Or you can try contacting iTunes Support via : https://support.apple.com/contact or https://www.apple.com/emea/support/itunes/contact.html