They want players to take responsibility for their choices so there's no trolling of the system. It's an unfortunate mistake but the placard would have clearly read "Available to free companies. Unavailable to private buyers" before you clicked on it to enter, and would have had a confirmation window that you were entering on behalf of your Free Company before you confirmed your entry.

You'll be able to claim your partial refund tomorrow after the new lottery entry period starts so you can enter for a personal then.

You may want to suggest to your FC Master that Land Acquisition rights be removed from all ranks so no would be able to accidentally (or with malicious intent) relocate the FC house. It's unlikely the FC is going to want to move for a while since it managed to get a large.