Non O based on what? Being over 50? You have the funds in a bank in your name? You don't need a TM30, you don't need a residence certificate. You probably don't even need a lease contract.
you can do an in-person report from 15 days before to 7 days after, you can do an online report from 15 days before to 7 days before, you can do a mail in report from 15 days before till whenever it gets there probably 7 days.
these courses aren't designed for convenience, the length is structured to satisfy DTV requirements of embassy officials at the MFA. Minimum safe bet course length is 6 months. Otherwise expect to be given a tourist visa for your 10,000 baht processing fee.
I screenshot everything through the process, including the final completed applicant details page, I have a complete record of my submission details. I suspect you were sloppy and didn't triple check everything.