Grateful for advice.

I will be cancelling my education extension, and will return to Thailand visa exempt (UK passport) . Question is :

do I need to take my passport to immigration to have the stamps amended?

If yes, and I am unable to do this on the day I depart Thailand (early morning flight), is it possible to do this a couple of days before departure - how long do I have to exit?

I recall reading somewhere there was a grace period of 24 hours, but cannot now find the reference.

TIA