What should a Chilean citizen do if they received a 45-day stamp instead of 90 days upon entering Thailand?

In american & same but I had connection to CM & b4 I realized it I was already boarding this that flight

So the MOST PRIORITY IS TO GO BACK TO THAT EXACT SAME OFFICER IN EXACT SAME AIRPORT & terminal & get him to take screenshot & write his error down & then issue the 90 day immediately

Then you keep that screenshot & his written & bring to immigration wherever you are

send them either back to the airport they stamped in at (If they are still in the city where they flew in to) OR to the immigration office in the area where they stay to get the stamp corrected.

Not Chilean, but the same happen to me. Got 30 day stamp instead of 60 days with a pre-bought tourist visa. Happened twice, once I noticed it at the immigration booth and corrected it there and then, once I forgot to check and had to go to immigration to get the stamp updated. They just hand-wrote the new date. All very easy and I get the impression it happens quite a lot, but records should be up to date digitally.

Go to immigration straight away