How can I extend my stay in Thailand with a METV?

I have a METV issued from US consulate valid from 01-may-2018 to 31-oct-2018. i arrived July 17 and first "admitted until" date is 14-sept- 2018. I think i understand if i bounce out and in before Sept 14 that will make new "admitted until" date of 13-nov-2018 But if i want to get more stay I should bounce in and out before 31-oct-2018 (valid until date) which should then take me to 30-dec-2018. Do i have that correct ? Then can i get a 30 day extension to take me through January ?