@Diane ******
all extensions of stays inside the country are sold as NO ENTRY :O <- that's because you're already IN the country when you get it.
An extension and a re-entry permit are totally separate things and require two separate forms (a TM7 for the extension and a TM8 for the re-entry permit).
Once you get your extension inked into your passport you then make the appropriate copies fill out the TM8 re-entry permit application and BUY either a single re-entry permit for 1000baht (that lets you leave/come back ONCE) or a multiple re-entry permit for 3800baht that lets you leave/come back all you want during the year your extension is valid for
like this;