Annual turnover

Reconciliation it and see where this difference is

It generally does not tallies due to reasons such as the SCHEDULE I Transaction ( Supply even if no consideration is involved ), which are recorded in the GST Returns but not shown in the Balance Sheet due to non-financial transaction. As per the Fundamental Accounting practises, Non Cash Transaction are not recorded in the Financial Statements.

So you have to reconcile them and find out the difference...

Reconcile your transactions to find out thr difference.

What if there is a wrong entry in the GSTR 3B

Then Retify it 

Madam if we rectified the mistakes in gstr3b but the FY of the previous year because Gstr9 has not been yet filed, so what is the solution or any suggestion