TurboTax will not automatically delete duplicate imports. The user is responsible to delete any duplicates when he/she reviews the return before filing. Additionally, if the user imports info from a tax document, he/she will not manually input the same info that has already been imported.
I'm so sorry you've experienced this issue. If you haven't efiled or mailed your return, you should be able to correct this duplication before filing. Otherwise, you'll need to amend your return. Do not amend your return until the initial return has been completely processed by the IRS and you've received any refund due (if applicable). When you are ready to amend, please see the instructions I'm sharing below (see link).
How do I amend my federal tax return for this year?
EDITED AFTER ORIGINAL ANSWER
*** I am NOT a tax expert. I am a seasoned TurboTax user, and volunteer to provide assistance to TT users. Nothing I post is to be considered TAX ADVICE; I bear no legal liability for responses.***
