@Miguel ************
the regular extension of 30 days is very unlikely to be denied.
I also did mine in Samui 11 days before current expiry with no issues. Have never been asked for a departure flight from there or Phangan for covid extensions (though I know never say never).
For a recommendation seen as you’re close, Phangan immigration are very relaxed in terms of extensions like this. Providing you attend the office in appropriate clothing, wear a mask and bring the correct information/signed etc I’ve never seen anyone denied thus far.