Who is "They"? If it is immigration that told you, I would think you should be fine. If it is your school telling you, then maybe they can give you a document to say there is a delay in processing? And in that case, just don't be in a situation to be asked for your passport/visa??
But again, this is a new scenario for me, so I wouldn't know
You probably want AoNang in Krabi, Hua Hin, Koh Samui, or Phuket. You could probably get away without your own transportation in AoNang, but really the rest, you will want your own transportation.