I can help you check why your tax appears to be at 10%, @josh-highcleredi.
Currently, there's no way to add or set up VAT in QuickBooks Self-Employed (QBSE). One thing I can think of is that the income and estimated tax is added as a line item when recording invoices. To change the tax amount, you can open the invoice created then update the amount equivalent to 20% of the sale/income.
To know more about how taxes are track and calculated in QBSE, open the details from these links: