how to create shell in this model?

this is the tutorial example in solidworks. Even though i followed the instructions I am unable to create shell with the thickness of 3 mm . can anyone help with this?
Accepted answer

Robert's got the right answer. I'm just adding an image to show the difference between your model and the tutorial.
Your model has a centerline running it's length, this is causing the Thin Feature Robert mentions.
The tutorial has a line (not a centerline). That allows the sketch to be "closed", and allows the Revolve feature to make a solid.