As others have said, the way the system is designed it cannot allow for backsies, since it would allow for plot manipulation and be open for bad actors to exploit it. Neither can they made an exception for any reason. After all, if they reverse your bid because of ADHD, who's to say bad actors won't also abuse it and pretend to have the same? The silver lining is if you don't win, you'll get 100% of your gil back. You only have to lose half if you win and don't claim. The other silver lining is that if you don't already have a house, you can at least enjoy that small if you win, then attempt a relocate in the next lottery period if there's a plot open you want still.

While your story is unfortunate and I can empathize with ADHD as I have a friend who has it, I can only suggest that you try your best to develop the habit of triple checking anything you do in-game that is a major decision. Like putting money into a plot, buying tome gear, etc to prevent another unfortunate event from happening.