apple maps walking driving mode

hello, i am a new driver that does not have the confidence yet to drive on the freeway so i stick to the roads. while using the apple maps on my iPhone, it plotted a course that went through the freeway, so i selected "walk" mode to stay on the road and avoid the freeway. however, after driving for no more than a minute, the app would automatically switch to drive mode and direct me to the nearest freeway. i kept selecting "walk" mode but it would switch to "drive" mode soon after. how do i prevent the app from switching to drive mode? or how do i tell it to avoid the freeway? i was very frustrated and surprised that the app would make the switch on its own. this could have caused an accident with all those unnecessary turns and stops to reconfigure the damn thing, especially for a novice driver!