Paid Turbotax for my 2018 return on 41419 but did not efile. I efiled today. How can I explain my late filing status ? I simply forgot to efile after paying Turbotax.

You have nothing to explain. 

If you are getting a refund there is no penalty for filing late.  If you owe tax due then expect a bill later for your penalty/interest.

if this is your first time filing late you can request the IRS to abate the penalties 

https://mybrokencoin.com/irs-penalty-abatement-reasonable-cause-letter/