Google Play is great at allowing you to request a refund for any purchase. They also have a PIN system you can implement on your device to help avoid any inadvertent purchase in the future.
To request a refund:
Click on this link: https://support.google.com/googleplay/answer/134336?hl=en and you should be able to start the refund procedure. If you are having any difficulties with it, you can always contact us to assist you or you can contact Google Play Support.
How to set up your PIN:
Click this link to get directed to the Android App Store and start setting up your PIN to prevent any inadvertent purchases: https://support.google.com/androidmarket/bin/answer.py?hl=en&topic=1100168&answer=1626831