Hello Claytonhousemeat
If the in QuickBooks balance correct but you know a transaction is missing the best thing to do is use the reconcile tool.This will show you if you have something duplicated which is causing the QuickBooks balance to be correct.If that is the case you can then remove the duplicate and create a transaction for the missing transaction using the + create icon.
If when reconciling the opening balance is incorrect or you can not see any duplicates just reply back here.
Emma