It has been my ultimate aim to get into an IIT!

But now

I dont know what happened I couldnt do well !

Is the only way left is that I should repeat the exam to get into an IIT?????

Yes , if this is your ur ultimate aim then there is no other way .. but i think u shouldn't be so negative at this point of time.. so better  .. Now study hard and if you get decent rank thn take admission in some good collage instead of dropping.