I didn't receive my second stimulus check so when prompted i filled in the amount i got for the 1st round The software incorrectly used my 2020 return amount to calculate

No, it cannot be changed.  

The recovery rebate credit is figured like the economic impact payments except that the credit eligibility and the credit amount are based on your 2020 tax year information. 

The economic impact payments that were received in 2020 were based on your 2018 or 2019 tax year information.  The economic impact payments were merely an estimate of what you would be entitled to when you filed your 2020 income tax return.  The good news is that if they overpaid you in 2020, you do not have to pay it back.  If they underpaid you, you would get the difference.  

Does this mean that people who received both stimulus payments could potentially owe money to the IRS because of the stimulus checks?

No, if the IRS overestimated a stimulus payment, you do not have to pay back the difference.