Since you received three W2's in 2021 the amount of income that you get taxed on is the sum of all three jobs.  When you add up the total taxable income from all three jobs you may have moved to a higher income tax bracket.  Also, if the third W2 that you entered did not have federal taxes withheld this would increase the amount that you owe to the IRS.  You can check this by adding up your total taxable income and federal taxes withheld from all three W2's and see if the amount withheld is less than your total tax liability.

Hope this helps!  Please let me know if you have additional questions on this topic.