Accidentally made an in app purchase

Strictly speaking all purchases are final (after all, you can't very well return them): please see this page for information on requesting a refund: Request a refund for an App Store or iTunes Store purchase - Apple Support

Apple do say in that page, 'You can't request refunds for recurring charges': however they have been known to be sympathetic in cases of actual error, so it's possible that they may allow you a refund as a one-off concession: but please be aware that they are under no obligation to do so: go to iTunes Store - Contact Us - Apple Support

Alternatively go to the page suggested in the Help page linked to above: Report a Problem