You can download or print your return to check your Schedule D entries.
You may have entered Capital Gains yourself, along with TurboTax moving Capital Gains to Schedule D from a stock sale, business property sale, K-1, etc. resulting in the doubling.
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When importing your 1099-B TurboTax will import all of the information provided by your broker. Your broker may have provided sales as well as summary totals for those sales. Check through your transactions to see where the doubling is occurring - you may only have to delete those summary transactions. If it has actually entered a duplicate of each and every sale that you had then you should probably delete the downloaded 1099-B and replace it with entries for the summary totals. After you have entered the summary amounts you'll be able to upload a pdf of the 1099-B that you received to attach to the return.