Did it say specifically that you did not pay more than half the cost of running your home, or did it show you a list of several possible reasons that you cannot file as head of household?
The only way that TurboTax knows whether you paid more than half the cost of running your home is that it asks you. One of the screens asked if you paid more than half the cost to run your home. If you mistakenly answered No, go back through the filing status questions in the Your Info section and change your answer. Read the screens carefully. The first screen will show your current filing status, and there is a box you can check to change it. But you have to meet all the requirements for head of household. Paying more than half the cost of running your home is only one of the requirements. See the first link in xmasbaby0's reply above for more information about the requirements.
