Hello and thank you for your question.
There are a slew of reasons that could be causing this. Income per books generally won't equal taxable income per the return and you reconcile the two on Schedule M-1 of Form 1120. You may have keyed in something incorrectly. Without looking at your books and what you've done, it's impossible to say.
Forgive me for being blunt now because I mean well. This is tax prep 101, staying in balance. If you are getting stuck with this "simple stuff" there's most likely no way you have the level of expertise to prepare the return. Get professional help. Just like buying a set of tools won't turn me into a mechanic, buying Turbotax and Quickbooks won't turn you into a tax professional or accountant, respectively, despite what Intuit's advertising might imply. Chances are you are (or will end up) costing yourself more in time, mistakes, and Turbotax fees than you are saving by not getting help.
Best of luck!
PS - I don't expect you to rate this answer at all, because we're unable to answer this type of question without reviewing your books and what you've done in TurboTax. Unless you can be more specific, and if so please do, there's not much we can do to help here.
PSS - I might be able to help you via an additional services offer if we set up a screen share and speak over the phone. You can activiate the screen share using join.me for free: https://www.join.me/ If you want to try something like that, let me know.