Coming to Thailand for 120 days. US passport gives me 60 days. Can I extend for 30 days and then another 30 days or do I need to do a border run. TIA

90 day report US passport. Not able to do on line even though I did last time (along with TM 30, etc). This is not the issue as I'm leaving for my O-A. Once returned with clean plate will start everything over. Due to this leaving for USA, I have some overlap. My notify of extension of stay is 17 sep 2019. I will border bounce on 18 to get 30 day stamp as I depart 15 Oct for USA. Now, I know you get 7day after to file 90 day. If in my review of this group, it appears the grace period does not include this 7 days to report OR exit the kingdom. I understand that I could exit on 16 but that would complicate things on my end (which then I will weigh my options).