How to fill form 231 for inter state purchase

Hello , 

I am filing online vat returns for my company and i have purchased goods from Gujarat (inter state purchase ) against C form , now i am having problem to fill value's in purchase section. i fill my purchases but its showing 2 % amount in my vat liablities. and as i know i dnt have to pay CST amount  then why its appear in my vat liablities total. please tell me whole process of filing form 231 for interstate purchase. 

thanx in advance 

Nikhil