When you buy an app like Print to Size, it can take a few days for Apple to charge your account and to send you an email. Don’t worry, though, it’s not a repeat payment, just a delay.
Print to Size is not a subscription
It is an old-school “paid app”: you can buy the app, and it is a lifetime, refundable, one-off purchase. Once you have purchased it is yours to use forever and you will never be charged again for it.
Check your App Store purchases
If you are not sure you can check your App Store purchases. To see how, here is a link to Apple’s instructions: https://support.apple.com/HT204088