Talk to your school, inform them so you can get your 90 stamp in advance if necessary. Then you'll need to pay for the re entry stamp at the airport. Don't waste your entire day getting your re entry stamp at immigration.
your putting other people's lives at risk then. Not carrying your passport doesn't harm anyone. In fact some hotels and most motorbike rental shops ask to keep your passport with your deposit. This is normal. Chill, my dude.