Dr note for Maternity leave

I live in canada (BC) and was wondering if anyone knows if I could get a Dr note to go on mat leave from a walk in clinic ? my dr office said i have to make an appointment to get a dr note and they cant see me anytime soon. and ive been planning on leaving work and going on my leave this saturday and thats been the plan for awhile. My manager told me i didnt need anything until now. now she wants a note 2 days before im supposed to leave. idk where to get a dr note.