Armaan and Ridz and their relation is all about first love and the realization of it... and lil takraars of it... and karva chauth has a underlying, dramatic intensity to it , when it is shown on tv.
Karva Chauth has the essence of janm jamaantar waala bandhan effect, which Armaan and Ridz sure may have... but it aint depicted everdyday that way on screen... for them it is realization of love and wanting to be with each other and karva chauth would be like suddenly portraying the whole relation on a different intensity level... which would take the mazaa outta it... I think...
the scene can wait until later...
Jus my 2 cents... no offence... the scene would a good one... but too soon.. and not in sync with the current intensity of their relation