I’ve been in Canada a couple of decades so I am more aware than your average Yank.
Still things are razor thin so it wouldn’t take much.
The government will have to go back to talks with the EU and try to tweak the deal and get cross-party support for it.
And if it decides a hard Brexit ultimately isn’t in the UK’s interest, it can trigger Art. 49 and cancel Brexit. It would have to do so before or by March 29 to stay in without further EU action.