No worries! Hopefully that bakery in West Hampstead has kept its quality up and not gone downhill in the last few years.
St Pancras, I see you're doing on the low level platforms. Good choice, considering your previous stations, but I would thoroughly recommend going upstairs and seeing the mainline station both on the inside and out. It's a magnificent building that deserves even a short look.
While on that note, have you considerered using the Southeastern HS1 services to Stratford International? They aren't cheap, but they are good fun, and the main reason I suggest it is that you could time it to be there when some Eurostars go through. I don't remember how much they cost right now, I'm sure they aren't included on a paper Travelcard though. Still, worth considering!
I'd also consider, while at St Pancras, walking round the corner to Kings Cross. Another station there worthy of a good look, it's much nicer than it used to be there. If it's a nice and dry day, the area out front could be a good place to stop and have a brew while soaking up the London atmosphere. Two stations done in no time
Paddington's trainshed is also worth spending some time admiring, although I am biased there as it is my favourite station anywhere in the world!
Overall I'd say the plan you have looks good, did I read correctly you're doing London the day before as well? So many things to recommend doing across London, but that's an entirely different thread as I could be here for a long time making my list! One of them though is something you may not have considered is a ride along the Thames on one of the Thames Clipper boats. Those things are mighty powerful, and when I did one a few years back the racket was incredibly fun