Hey, sorry for the confusion. I was perplexed as well.
I have Vietnamese passport and initially with everything I read online + my school's advice, I assumed upon arrival in Thailand, I would be granted visa exemption.
At the airport I was stamped in from 8/8 to 6/9 (29 days). The stamp was in Thai and I couldn't read it well. As this was my first time entering Thailand without a visa, I thought that was the visa exempt.
But now after clarifying with the school admin and visa agents, I realize the stamp reads "ผ.ผ.30" (visa waiver), not "ผ.30" (visa exempt). And I've been told visa waivers cannot be extended. So now my choices are the ones mentioned in the original post, or if you could suggest another way to go about this, I would greatly appreciate it.
I've updated my post for clarification.