Solved
This was my first year renting my home, and it started exactly mid-year. So when I enter the amounts, Turbotax correctly divides the insurance, taxes, interest in half--this makes sense.
But it is -also- dividing the repairs, maintenance, and supplies I purchased during the rental in half. This is improper--those are entirely related to the rented period and should be counted 100%. How to correct this other than overriding the shedule E manually, and actually, how do I even do that in turbotax online?
Shared expenses will be pro-rated based on the number of rental days. Expenses that are specific to the rented portion of your home should be entered on the page titled "Any Miscellaneous Expenses?". Entries made on this page will not be allocated.

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