As HypnoticShark mentions, it sounds like your Matinee isn’t getting triggered. You can do this via Blueprint as noted above, or by selecting your Matinee and enabling Play on Level Load via the Details tab.
Have you set up a director track? The director track controls which camera is active and the player is looking through. The director track can be added in the matinee by creating a director group (this should create the director track automatically). Set a keyframe and choose the camera group you want to use.