The IRS relies on the 401(k) plan to distribute the correct amount for the amount of contribution being returned. Regardless, $600 is to be included as income on your tax return because that is the amount of the excess deferral that was originally excluded from box 1 of your W-2 (which would not have been had it not been deferred in the first place).
Whether not it is permissible to separately include a negative $30 entry as Other income is questionable. Those who suggest this are relying on a ruling that pre-dates the establishment of miscellaneous deductions subject to the 2%-of-AGI floor under which this would probably normally be claimed. Miscellaneous deductions subject to the 2%-of-AGI floor were suspended by the Tax Cuts and Jobs Act of 2017 until 2026.
