I didn't actually mind this episode as much as the one before - which I found really clunky.
I thought the mix-up was a bit odd, and I didn't really get why Sister Evangelina was having such a break down over it - it didn't seem quite in character.
The thing that really struck me as out of place, though, was the Patsy's girlfriend saying she wanted to be married to her. I could be wrong, but I can't see someone saying that in 1960. The same emotion, yes, obviously, but not with reference to a legal change that must've seemed unimaginable then. Did love the 'we don't like cake' bit though. 
It does make me think how fast things have changed.