So you've decided to try a free trial of Wallet Premium, great decision! Your trial will end after 14 days, at which time your Wallet app will become Premium, and you will be charged the appropriate price for a yearly Starter Premium plan for your region. You can cancel this through your GPlay app or Google Play Store account, under the Main Menu > Account >Subscriptions > Wallet trial > Cancel subscription.
You must cancel BEFORE your trial ends to not be charged for Premium.
*Please note, Wallet's free trial is the Starter Premium version of Wallet, which allows two bank-connected accounts. You can choose to purchase the Master Premium to have unlimited bank connected accounts and Group Sharing.