Not sure what passport you are holding. I was at the Mae Sai border once and the immigration officer didn't know that either, went to the supervisor and there was a such a thing as a 90days tourist visa.
Did you count arriving 2days later depending on where you are flying from?
The ask:thailand community, consisting of multiple Q/A groups with over 100,000 members, powers this platform. It is not an official government resource. Our members actively contribute to this resource, and while we strive for accuracy, we cannot guarantee its complete reliability. Assistance to travelers is provided as a community service.