Arrival stamps are not visas, they are visa exempt stamps.
Some countries are 15 days only some are 30 etc.
If you want actual 60 days it is called a single entry tourist visa that you apply for from outside of Thailand from a Thai Embassy or Consulate before coming.
cant stay forever on tourist visas, there is a reason there is multiple visa options for different purposes. This was always going to happen to you at some point.