Once you entered all of your income, it sounds like your tax bracket went up or you did not withhold enough taxes on the rest of the income you entered. Refunds or taxes due can change with every additional input on your return. What you see after you input your first item will typically not be the final result. In addition, the Recovery Rebate Credit is based on your total income for 2020.
Per the IRS, your Recovery Rebate Credit amount will be phased out if your adjusted gross income for 2020 exceeds $150,000 if you are married filing a joint return or filing as a qualifying widow or widower, $112,500 if you are using the head of household filing status, or $75,000 if you are using any other filing status.
Did you get the first or second Stimulus payment? And enter the amounts you got?
Yes you can see your refund or tax due change when you enter the Stimulus payments. Your 2020 return starts out by assuming you didn't get any Stimulus payments so it gives you credit for the full amount. Then near the end you enter how much you actually got so it only gives you the difference if any. You don't get it twice.