A self-employed retirement deduction is a personal, above-the-line deduction, not a deductible business expense. Only retirement contributions for non-owner employees constitute a business expense. Because self-employed retirement contributions (for yourself) do not lower your net profit, they do not lower your self-employment taxes.
I assume that you have sufficient net profit to cover the deductible portion of self-employment taxes and the total of your self-employed retirement deduction since you said that adding the profit-sharing contribution changed the tax liability your state income tax return.
Another possibility on your federal tax return is that you have non-refundable tax credits such as a Retirement Savings Contributions Credit and your income tax liability (Form 1040 line 22) is already zero without the profit sharing contribution, meaning that even without the profit-sharing contribution your tax liability already consists only of "other" taxes such as self-employment tax that are not reduced by any retirement contributions.
