How to cancel the pre-registered domains?
As long as a pre-registration is not prepared to be registered (which is shortly before the opening of the General Availability), you can delete the pre-registration from your account and you will not be charged.
In order to delete the pre-registration you need to follow the instructions:
1. Go to New gTLDs overview
2. Mark the pre-registrations you want to cancel.
3. Click on Delete selected domains on list