If your investment income on T3 or T5 slips and is the same as the "summary" your financial advisor or institution provided you, only make the entries on from the slip on the T3 or T5 entry screen. It's quite common for a summary page to accompany these slips and you do not need to enter it again, as you are indeed doubling your income.

You'll need to return to the Investment section of your TurboTax program and delete any double entries if you have entered them.