Get slicer to follow contours
What do you mean by not follow the contours ?
Your little picture shows 2 perimeters (one external and one internal) with infill between. If you are using profile that is anywhere near default then the infill pattern will be set to Rectilinear which is the pattern shown between the perimeters. As such its doing exactly what its designed to do.
You can change infill pattern to be something else like concentric (which would follow the perimeters as far as it can) but the advantage of rectilinear patterns is that each successive layer is printed at 90 degrees to the previous. This gives a crosshatch structure which makes the part much stronger. If you printed with concentric you risk the part being very weak and falling to bits.
Rectilinear is also quite quick to print compared to most of the other option too so its the best balance of speed and strength.
Thanks! I found the concentric option and it does look "better", but it is not faster. I expected it to be faster as the extruder doesn't have to accelerate as much, but as you say, rectilinear is just a little bit faster.
@ak-1 do you perhaps mean nonplanar?