Need advise for US citizen traveling to Thailand

I plan to come to Thailand on a 60-day tourist VISA but later while in Thailand I will apply for a 30-day extension….so I can be there 90 days. 


my concern is will Thai  passport control allow my entrance on the 60-day Tourist VISA when my return flight is 90 days out?


my other concern is when leaving USA will the airline accept my 60-day Tourist VISA with 90-day airline ticket.


i did check with Washington DC Thai Embassy and they said no problem to get the 60 day VAiSA with the 90 day airline flight ticket.


your advice and experience would be appreciated.


jim yager