Has it been less than 48 hours since your purchase? If so you can request a refund directly through Google Play by following the instructions in the link below:
If it has been over 48 hours, you can send us a refund request via our contact form. Your request will be reviewed and a decision will be made according to our own internal policies. Please include the following details:
– Order number (GPA) of your purchase. This can be found in the confirmation email sent to you by Google upon making the purchase. If you can no longer find the email, please follow the instructions in this Google Store Help article – https://support.google.com/store/answer/6160235
– Reason for the refund. Please be as detailed as possible!