If you are in a hotel in a spanish speaking country and you would like to announce your departure the next day you should say:

Me voy mañana

or in case you are with someone else you should say it in plural

Nos vamos mañana

If you are not leaving the next day but in one/two/three/four days or 1week you say:

Me voy dentro de un dia/dos dias/tres dias/cuato dias/ una semana