If you arrived to Thailand 24 September your 60th day was 22 November and that was also the first day of the visa extension. So you have to fly out the 21. December. Check the date of your visa. From 2 January to 25 March that's ok if you have a new visa and you ask the extension in February.
We made the same more times, but flying to Penang, Malaysia after 60 days and then flying back to Thailand. We didn't even have the ticket to Malaysia before the first arriveing, but the proof of the hotel reservation.
You will not have any problem with your return flight ticket. I have a 5 months return ticket and I have a 60 days tourist visa. It will be your choice that you will applied a visa extension after 60 days or you will leave Thailand and you will come back.
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