"I had just one transaction for form 8949."

You are asked to mail Form 8453 and Form 8949 because you told TurboTax "I'll enter a summary for each sales category" instead of "I'll enter one sale at a time."  The "concept" behind "I'll enter a summary for each sales category" is that you have so many trades that entering them one at a time would be too onerous. 

Delete that trade and that broker and start over.  Click on the right radio button this time.

Tom Young