Are you saying that as soon as you click to Get the app, that your account is immediately charged for a year's subscription?
If that were the case I doubt that it would be such a highly rated app. If that were happening there would be many complaints in the reviews.
A trial subscription must be canceled 24 hours before the renewal date, or it will renew as a paid subscription. You would have needed to cancel the 3-day trial in your Apple Account details before the end of the 2nd day so as not to be charged for the year's subscription. Deleting an app will not cancel a subscription.
M1 Mac mini, macOS 15.3; Watch, series 10 GPS-only, watchOS 11.3; iPhone 16, iOS 18.3; TV 4th Gen, tvOS 18.3; HomePods, audioOS 18.3 and Airport Express w/ Airplay 2