Kindly note that the P&L in the backtest will only reflect the completed trades and will not reflect the profit or loss of an on ongoing trade. As backtest is used to check the performance on the historical trades only. Also, P&L in the backtest can be calculated only after the exit price is established based on the exit conditions in the strategy created.
In your case, the P&L reflected in the backtest (i.e, -12,000 INR as loss) is calculated only based on the 3 completed trades.
As explained above, P&L in the backtest can be calculated only after the exit price is established based on the exit conditions in the strategy created. However, in Paper Trade for NRML/CNC trades, the P&L is a reflect of the executed trades and the ongoing trade as well. In Paper Trade, the P&L displayed will be dynamic as it is calculated based on ongoing LTP. Therefore, the P&L of Backtest and Paper Trade cannot be compared till the trades are closed, although the P&L in both are correct, but will have differences for the reasons explained above.