Once you activate a free trial through the Google Play store, you will need to cancel at least 24 hours before the trial ends to avoid being charged for the annual subscription.
Please note, you will need to cancel through the Google Play store settings on your device.
Open the Google Play store app on a mobile Android phone or tablet
Tap the menu button in the top left corner of the Google Play store app (3 horizontal lines)
In the side menu that appears, tap the Subscriptions option.
Tap the fieldmargin free trial subscription that is listed there.
If you do not see fieldmargin listed, this means you do not have a free trial activated on this Google Play account.
Tap the 'Cancel subscription' option and follow the on-screen instructions to confirm cancellation.
If you run into any trouble, this Google Play help article includes additional details for cancelling your free trial.