valuation of closing stock

as per IT Act only

Firstly it depends on whether you are eligible for GST input tax credit or not. If yes, do not include GST amount. If no, you should include such amount since it will be your cost.
Secondly, when the question is about reporting an item in the Balance sheet of the assessee, it has to be as per AS/ Ind AS, as the case may be.
So, for balance sheet, your closing stock should be as per AS-2, also see the first GST ITC criteria.
But for 3CD reporting under ICDS, it should be as per section 145A, i.e. inclusive of GST