I've always read that you should never book through an agent like Agoda or Bookings for the Thai Pass, but book directly with the hotel of choice. Can you cancel and book directly?
I got an O-A many yers ago and never had to have anything notarized (US citizen). Not sure how you could it notarized anyway if it has already been signed. A notary has to certify the person's signature so it has to be signed in their presence.