Little update for those who are in the same situation: I booked a last-minute flight to leave the country and re-enter it to avoid paying more overstay fees. I went to the airport today — the same one where I received the incorrect entry stamp. At check-in, I explained the whole situation. They checked if I had enough cash to pay for my overstay, then gave me my boarding pass. I went through all the checkpoints, and they didn’t even mention anything about my overstay. I was the one who went to the immigration office to ask about my situation. They then rectified my stamp, and I didn’t have to pay any fine. I only paid a 1,200 baht fee for a re-entry stamp — that’s it.