DTV reset- land border

I have a DTV and am using a land border run company to go to Cambodia. I actually have been in Thailand less than 90 days on a visa, but I am planning to exit because I did not get a visa for my young child, who entered visa-exempt. I did not get the DTV for her at the same time I did because I don't plan to use the DTV much longer than a few months at a time. I am using the land border company because it is the most efficient way to get a new entry stamp. However, I've been informed that the border agent has never encountered a DTV visa and will charge an extra 1500 baht for an entry stamp for 180 days. Their reasoning is that an entry stamp for a longer period should cost more than the base fee . I objected to this but the visa company says they cannot override the border agent's decision. I may just overlook this as unfamiliarity with new visa and pay it to avoid any problems. Just looking for advice on this or advice on if it is even a good idea to get a new 60-day stamp this way.

I couldn't find this in a recent search but can I cross to cambodia by land border to get my visa stamp and come back a day or two later? I have to leave by March 24th. Also I know I need a PCR or APK test. I thought they were one and the same. Can I buy this at my local 7-11 and take it in front of them or do I have to go somewhere and do it so there is a record of when I took it? Time is not on my side here.