@Sophie ********
IF you're a passport holder from a visa on arrival country ( 1. Bhutan: Kingdom of Bhutan
2. Bulgaria : Republic of Bulgaria
3. China: People’s Republic of China
4. Cyprus: Republic of Cyprus
5. Ethiopia Federal Democratic Republic of Ethiopia
6. Fiji
7. Georgia
8. India
9. Kazakhstan: Republic of Kazakhstan
10. Malta
11. Mexico : Republic of Mexico
12. Nauru
13. Papua New Guinea
14. Romania
15. Russia : Russian Federation
16. Saudi Arabia:
17. Taiwan
18. Uzbekistan
19. Vanuatu )
You CAN NOT extend the visa. You *MAY* (if the immigration office is willing) to get an extension of stay denied stamp, which gives you 7 days to leave Thailand. You should apply for that on the second-to-last day if possible, because the extension of stay denied stamp begins on the day you acquire it.