The GMs would be swamped with refund requests if players could contact them to withdraw their bids for whatever reason.

If players were allowed to withdraw bids on their own during the entry period there would be a fair amount of trolling occurring, making the process even more irritating for those trying to get a house and failing.

That's why the Purchase Guide on the Lodestone clearly states:

Entry Period
In order to submit an entry, access the placard of an available plot during the entry period and proceed with the submission procedures to receive a lottery number.
* Once submitted, a lottery entry may not be withdrawn.
While I do have some sympathy for you (we all make mistakes at times), as others have said you should take this as a lesson. Wait until you can focus before engaging in actions that can't be reversed. I know you mentioned ADHD but unfortunately too many people who have never been diagnosed with it and probably don't have it use it as an excuse for their actions so it has lost its meaning (which is sad for those who truly do have ADHD).

Hopefully, someone else will win the plot and you will get all of your gil back then another medium will appear in the next lottery period for you.