If I closed a 'doing business as' name at the end of 2017 and have a new dba name for 2018, do I need to change anything on my 2018 return?

The one for 2017 should have already been reported in your 2017 tax return as closed by answering YES to “Is this the final year of business?”

Therefore, the new 2018 name should be reported as such with the new name for 2018.

Keep all information pertaining to the name change, as well as all expenses and income incurred for each, in case the CRA requests it later.

If I missed answering that question should I be revisiting the tax return and refiling?

There is no need to refile your 2017, just make sure you have all documentation in case the CRA requests it later then you can explain it to them.