Get your taxes done using TurboTax

With a solo 401-K, your contributions can consist of two types of contributions, an elective deferral and employer non-elective contribution. 

The elective deferral can be up to 100 of compensation, and the employer non-elective contribution is up to 25% of compensation. However, in the case of a self-employed individual, compensation is considered to be net self-employment income after deducting 1/2 of self-employment tax and contributions to yourself. That may be why you are over contributing, you may be overstating your self-employment income.