3 posts about wrong stamps.
PLEASE check your stamps directly if your passport is returned to you. Mistakes are human, yes even Thai Immigration officers are human beings.
Correction are quickly done if you notice it directly.
If not, visit your local Immigration office, wait in the queu and get it sorted out.
If you got a longer stay, DO NOT even think of staying that long, you are in overstay from the day you should be stamped in. It is YOUR passport and YOU are responsible for checking the stamps and make sure it is correct.