Hi HeidiHilleard,
Have you reconciled your bank accounts in QuickBooks to the end of the VAT quarter to ensure that all transactions are entered with the correct date and VAT code?
We'd recommend doing this to ensure you have all transactions entered for the period and that there are no missing or duplicate transactions impacting the VAT.
You can view our reconciliation hub here for how-to guides if you have not done this before.
Thanks