Happend at home in Aus. I wouldnt worry about it, I have heard of other people who were asked and just booked a flight on there phone at the checkin counter and all is ok.
They may ask to see a ticket out of thailand within 30 days if you are flying in without a visa. But I would suggest trying to check in first if you dont have a flight out already. If they ask you about it, you can book a cheap ticket then and there with air asia to KL (or another super cheap destination)
Once you leave Thailand your current visa exempt will be canceled/finished. If you only stay 22 days it does not matter you get stamped out when you leave.
When you fly back in after however long you will get a new visa exempt stamp.