Hey LaurenDoig
Thank you for your request.
If you have bought a day pass, then it is valid for the whole of Switzerland. If you want to be sure if you bought the right ticket, I recommend you to contact our Railservice.Tel: 0848 44 66 88 CHF 0.08/Min.
On the online timetable you can check the occupancy of the trains at any time. If there is a large occupancy, then I recommend a seat reservation.
Greetings, SandrineS