You might need to amend 2018 and 2019 to get the right amount to enter on 2020.
You have to report the carryover every year until it's used up. You can't skip a year. Even if you don't report it on your return you have to reduce it by the 3,000 (1,500 MFS) when you carry it over to next year. You can't choose when to use it.
