I need to review my schedule C for my farm. I can't efile my federal return without fixing the entry.

Farms are usually reported on a Sch F ... but you can (and should) review the entire return prior to filing.  

• After the return is open, click in the left menu column on TAX TOOLS, then PRINT CENTER.
• Then choose "Print, save, view this year's return."
• The next screen should offer some options:  "Just my tax returns", or "include government worksheets (optional)", or "include government and TurboTax worksheets (optional.)"

depending on the type of income farming income either goes on form 4835 or schedule F not schedule C.

the concept of business basis doesn't really apply to a sole proprietorship since any and all of your personal assets are at risk (thus part of your basis).  you are at risk to the extent the FMV of all your assets exceeds the value of all your liabilities.  

If you had "assets" that were being depreciated and the business percentage varied from year to year, TurboTax does not really support reporting the sale of that "asset".  You must MANUALLY calculate and enter things under the "Sale of Business Property" section.