I assume that because you mention Net Earnings, you are a sole proprietor. With no net profit, no solo 401(k) is permitted. Unless corrected by a proper return of excess contribution, the contribution is subject to a 10% (not 6%) excess contribution penalty on Form 5330. TurboTax does not support Form 5330.
You need to ask the brokerage what you need to do to obtain a return of the excess contribution.
