Why not just cancel via hhonors website or call the hotel directly yourself? I've double booked myself at least twice in since September (once at the same property) and canceled online with no problems. When the blizzard shut down the midwest I canceled one reservation online and called one hotel just before check-in time and rescheduled with no problem (granted my rate was cancel by 6PM day of check-in).
If you are three days out why not just do it yourself????