Hi everyone!
Sorry for being such a Uni noob, but if anyone could help me out it would be much appreciated.
For BSci first year, are all the big subjects' lectures in a class stream? E.g if I register for a chem, bio or calculus lecture at 10 am on Monday, will I have to do the 10 am on Wednesday and Friday as well 
Hadn't accounted for that in my mock timetable so a little bit stressed 
Depends on the subject sometimes. In bio psych I could register in one lecture at 4:15pm one day and 2:15pm the other; i.e. they weren't 'streamed'. However, in that event that it does force you into a stream: do not stress. Nobody checks attendance in lectures, and it's very unlikely that they will get filled to 100% capacity if you get there on time.
As a result, you can rock up to most lectures for subjects you're not enrolled in, and especially 'alternate streams' that you're not necessarily registered in. Nobody will be walking around to make sure you 'belong there' (so to speak) in 1st year science lectures.
You should be fine. Hope this helps.