After you file

Yes, you are correct, you should not be paying any tax.  

First, I recommend deleting all entries related to the 1099-K you have already entered. ‌Check 1. 1099-K input, 2. Self-employment income & expenses and 3. Investments and Savings for any data related to the 1099-K and delete.

Next, follow these steps in TurboTax Online:

• Within your tax return go to the magnifying glass icon on the top right, type 1099-K and select the Jump to 1099-K link in the search results
• Choose Add a 1099-K
• The next screen will ask "Which type of income your 1099-K is for?" choose Personal item sales, then Continue
• Enter the information from your 1099-K
• After you choose continue, the next screen will show "Personal Item Sales". Here is where you choose "All items were sold at a loss or had no gain"