Do I need to amend my 2018 return to fix this?
Yes. After you amend the 2018 return, then (and only then) can you start your 2019 tax return. Otherwise, if you start the 2019 tax return before amending the 2018 return, the amended changes "WILL" "NOT" be imported into TurboTax 2019.
it put it in a 40 year deprecation.
That's because you may have selected the wrong thing, unless your rental is not residential, but is commercial real estate.
Residential rental real estate located in the U.S. is depreciated over 27.5 years.
Commercial rental real estate located in the U.S. is depreciated over 40 years.
