That's right. If you have self-employment income you can only contribute up to your net profit reduced by the deduction allowed for the ER portion of your self-employment taxes. The 1/2 SE Tax amount will be on Schedule 1 line 15 which goes to 1040 line 10.
See IRS publication 590A page 6 about self employment income (it applies to both Traditional and ROTH IRAs)
https://www.irs.gov/pub/irs-pdf/p590a.pdf
