Your carry over deduction is from 2018. Not 2019. If you were not able to use all of your carry over from 2017 on your 2018 return, then the remainder is carried over from 2018 to 2019 - not from 2017 to 2019.
If you did not use the carry over on your 2018 tax return, then you have to subtract the amount you "should" have used on your 2018 return and the balance is what gets carried over to your 2019 tax return.