The only thing to do is wait for the IRS to recalculate your return and adjust the refund. If you will not be in a balance due and want to pay it by April 15, 2021, see: How can I pay my federal taxes?
For more information from the IRS, see: March 1, 20201 Update for 2020 Recovery Rebate Credit — Topic G: Correcting issues after the 2020 ta...
Yes, you are eligible for only $600 for the second stimulus. The stimulus payment section must have amounts entered in each stimulus payment box.
For more information about your initial question, see: What is the TurboTax 100% Accurate Calculation Guarantee? This guarantee exclusively covers TurboTax calculation errors.
