Form 1040 Line 12b programming error

We are taking the standard deductions so we should be able to deduct $600 (married filing jointly) on line 12b on Form 1040 for Charitable Contributions.  However, TurboTax automatically puts $300 in the block.  When I run error check it flags every time and when you look at the form list, there is an error on 1040/1040SR Wks.  I've tried manually entering $600 but it overrides it every time and puts the number back to $300.