You are getting taxed twice on the income reported on Form 1099-NEC. Since the income is from self-employment, it is subject to both income tax (being added to your other income) and self-employment tax (added to your total tax). The situation you are seeing on your return is correct as you described it.
Since you are self-employed, you do not have an employer that is withholding Social Security and Medicare tax from your income. If you were an employee, these taxes are automatically withheld from your wages and submitted to the government by your employer. Half of the amount is paid by you through withholdings from your wages and the other half is paid by your employer.
When you are self-employed, you are responsible for paying the full amount of Social Security and Medicare tax. This is done in the form of Self-Employment tax and it is collected through filing your tax return.
To learn more, take a look at the following TurboTax article: What is the self-employment tax?
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