Hi Persefona, thanks for joining us here on the Community. 🙂
The best way to rectify a discrepancy between the bank balance is to reconcile the account against bank statements - as the difference is a large amount, first check that a beginning balance was recorded for your bank in QB (this is the bank balance at the date when you began recording transactions in QuickBooks).
This balance would be the first transaction entered on the account, and you can check this by going to the Cog > Chart of Accounts > Select 'Account History' beside the bank account > click the 'date' header to re-order the list from oldest > newest.