@Anthony *******
pretty much.
You MIGHT be able to go in on the last day of your current stay and apply for any extension, and if they want to accept the application (they can refuse), they'll give you an Application Denied stamp with 7 days to leave to Thailand. We generally tell people to avoid this if possible because it can affect your chances of entering Thailand or other countries in the future. If you apply on the 14th that stamp would be valid for 7 days (counting the day you receive it as day 1) March 14-20.