eCheckin really doesn't mean anything... The front desk has the option to give away your room if they want/need to do so. You do need to be present to complete the checkin process and get a key. Until that happens you haven't been there. Even sending someone in your place, if you have a friend or family member near the property, may backfire if they want to see you to get your HHonors benefits. Some properties have been reported not being so strict, but you know if you really need the night to count they will enforce every little rule they can.
Good luck on getting your last room.