You will not be banned. I have overstayed twice. First time was 1 day and second time was 2 days. I payed the fines and was allowed back into the country with no problems. It's 500 bht for each day over .
And you're dead sure about this ? I would hate to arrive at Suvarnabhumi airport and they tell me I need to miss my flight and do the test first. This has happened to me before.
The documents you need for test and go is your passport, vaccination certificate, prrof of booking and payment for 1st and 1 night only in an approved hotel, insurance certificate and PCR test no older than 72 hours.
I overstayed 2 days and was allowed back into the country. If you pay the fine then you're good to go. Though there is a certain amount of days that if you overstay then you will be banned for a year