It sounds like somehow, TurboTax recorded that the entry was made twice.
Your best course of action is to delete all traces of the form that reported tax-exempt interest - the 1099-DIV or 1099-B and all related worksheets. To do this for TurboTax Online, follow the instructions below. Then type the form in by hand.
If that doesn't solve your problem, please write back.
https://ttlc.intuit.com/replies/3288508
