Calculation of Social Security earnings

TurboTax correctly placed my $300.00 Charitable Contribution on line 10b of my 1040-SR return reducing my adjusted gross income; however, it also placed the same amount on my Social Security Benefits Worksheet on line 6 effectively reducing my Taxable Social Security benefit noted on line 6b of my 1040-SR by $255.00 which I feel is "double dipping" the contribution for tax purposes.  Any reason the $300 cash contribution would also reduce my taxable social  security earning amount or is this an issue with the TT program?