How can I cancel a pending purchase

Hello there, Chissy_beauty7.

For cancelling a Pre-Order the following Knoweldge Base article has the information you're looking for:

iTunes Store: About Pre-orders

http://support.apple.com/kb/HT5714

Specifically:

To view, cancel, or see the expected release dates for your pending pre-orders

1. Choose Store > View My Appie ID, then click Manage Pre-orders, which located in the Settings section at the bottom of the Account Information screen in iTunes on your computer.
   
2. From the Mange Pre-orders screen, click the Cancel button to the right of the pre-order item you would like to cancel. You'll be asked to confirm your pre-order cancellation.
   

Thanks for reaching out to Apple Support Communities.

Cheers,

Pedro D.