Not to worry! If you have a Pay Later reservation and park at a different location, you will not be double charged. At checkout, you will only pay for the time parked. Your reservation rate will not be valid since you are parked at a different location.
If you have a Pay Now reservation, you will be able to apply the amount you prepaid as a credit towards your stay at checkout. In order to do so, please make sure you scan your reservation, Spot Club card or app at both check-in and checkout. If you pulled a ticket at check-in, please see a cashier at checkout and provide a copy of your reservation.