After you file

Yes, with the additional information you provided, you are correct that you will not be taxed on the receipts from your 1099-K.  If the gift was from your mother (note if it was more than $18,000 your mother may need to file a gift return), then it isn't taxable income. 1099-Ks aren't required over $5,000, but can be provided anyway. 

You can indicate this in TurboTax Online when you enter your 1099-K. Choose the option "This amount in box 1a is too high, and enter the amount of the gift. For example if the 1099-K shows $1,000 in box 1a, report the $1,000 in box 1a, check the box that the amount is too high, and enter the full $1,000 as the amount that shouldn't be included.