I did my TN recently (did a flagpole)..Drove from US, crossed the Canadian border, informed them i am turning back to US, took a U-turn (did not enter Canada), got my new TN and reentered US.
I informed CBSA, Public health Canada and my state in advance and also did a Covid test as a backup.
You can check up with CBSA and Public Health Canada mentioning you are not going anywhere out in US, finishing your TN and entering Canada back and if you need to do ArriveCan and need to follow 14 days isolation.
3 days and 2000$ quarantine is only for flight passengers.