It would be the difference between what you contributed and what you distributed. You start with your contributions, $13,200 in this case, and then you subtract the amount you distributed, but not any portion of that that included earnings. Since you distributed less than you contributed, then there were no earnings distributed.
"The only DISTRIBUTION I have taken from it was in 2024, for $9,975."
TurboTax (TT) is determining how much of your $9975 2024 distribution is taxable. Since this is your first distribution, ever, the answer to the question ("What were my net regular contributions prior to 2024 that remain in my Roth IRA?") is $13,200.
In future years, the next time you are asked that question, the answer will be $3225 (13200 - 9975 = 3225). None of your 2024 distribution will be taxable since it consists 100% of prior contributions; no earnings were removed form the Roth account.