To get the KR22, you’ve got to notarize your US marriage cert, get it authenticated (state + US Dept of State), legalized at the Thai Embassy in the US, then once in Thailand translate it, certify it at Chaeng Wattana, and finally register at your local Amphur. I forgot to do all this before coming here and it gave me a big headache, so definitely sort it out first!
Maybe the agent just wants proof of the 20,000 baht. I don’t know could be a miscommunication. If you come back, I’d suggest getting the Non-O visa again when you leave the country. Using the 60-day exemption too often might cause problems next time.
You might want to consider the K1 visa, which gives you 90 days to get married in the United States. My husband and I got married when we were in our 20s, and we were both quite young at the time. I had just graduated, and my husband was in the Navy, earning a modest income. He did pay taxes, though! If you pay taxes and can provide proof of income, that will help your case. I'm not entirely sure how much you need to earn to be eligible, but you can also include co-sponsor income to meet the requirements. Additionally, having no criminal record is important for the application process. Just keep in mind that you may need some money set aside to cover the paperwork. I believe the K1 visa is the best route to take. Avoid the tourist visa, as it could end up being a waste of money. Good luck.