Deductions & credits

I finally was able to get the correct amount to show for line 12b on form 1040-SR for married couple filing jointly.  The problem now is that line 12c is to be the total of 12a plus 12b.  It shows noting on the copy to be e-filed with the IRS.  In the past if a line was to be completed and left blank, the IRS rejected the return.  How do I get the total of 12a and 12b to populate onto the tax form?  It shows on the worksheet, but not final form.  Wasted too much time trying to get this charitable deduction corrected when TurboTax should have corrected the software error.