I should list my single-member LLC as a disregarded entity on Schedule C. TurboTax keeps “correcting” me and listing the entity as a partnership. How do I fix this?

If you are a single member LLC, you should not be using TurboTax BUSINESS>  You should be using TurboTax Home and Business or TurboTax Premium online.  If you are a single member LLC and did not elect to be treated as a S- Corp, you would be filing a Schedule C instead of a 1065.  A 1065 if a partnership return. 

If you are using TurboTax Business, you will need to switch to Home and Business or Premium. 

If you chose to be treated as an S-Corp then you would file form 1120S using TurboTax BUSINESS.