Having trouble marking sharp cornered cutout...

I am new to Blender and 3d for that matter. I have been attempting to follow the Jaguar tutorial by SpeedTiti. I have posted my progress. My problem is with the back cutouts. Even if I extrude several times in, and then twice down, the SubSerf feature rounds the corners. How do I make the cutouts so that they are sharp? Any advice would be appreciated!

Please see the picture to see what I am talking about. I can’t figure out a way to replicate what the tutorial shows. (Fig. 3).



Tried adjusting the weights?

select the verticies and hit Shift-E to add creases. also adding more verticies will sharpen the edge.