My question is that should i join dummy or not. Cant it be the preparation for iit with normal schooling ?

dear abhinav 
no , donot join dummy school . you can do best preparation in regular schooling , it will be better to prefer cbse schools as u will read ncert textbook their , 
and one more time it helps for revision in school . 
and 2^nd thing – u will get bored in home studying everytime , so, in school u will refresh your mind , 
HOPE IT CLEARS 
REGARDS