I believe that you lose your money if you cancel it. Rescheduling is your best option even if its 100$ fee.
This is straight off their site:
"Rescheduling Testing Appointments
Rescheduling your testing appointment will result in a rescheduling fee.
A candidate who wishes to reschedule his or her testing appointment must contact Prometric in advance of the testing appointment and pay a fee directly to Prometric. The fee schedule is as follows:
Rescheduling Fees
$100 One to five business days prior to the testing appointment
$60 Six to 30 business days prior to the testing appointment
$25 31+ business days prior to the testing appointment
**Saturdays, Sundays, and holidays are NOT business days**
Appointments can be rescheduled by calling 800.688.5804 or through
www.prometric.com. Leaving a message for a local test center is not sufficient; the local test center cannot schedule, reschedule, or cancel your appointment.
Canceling Testing Appointments
If you cancel your testing appointment and do not schedule another exam within six months, the cancelation will result in a complete forfeiture of your examination fee (as noted in Step 2 above, examination fees are nonrefundable)."
