How do I scale a letter how it should be? I would like to extrude &amp; scale the outter edge of my letter like this :

but Actually it looks like this ...

I have no clue how to do it ...
Also  there is another problem,  if I scale a mesh is there a way to deactivate the z axis ?
To deactivate $Z$ you can scale pressing S followed by Shift + Z.
$X$ and $Y$ will still scale.
Also the transform panel have little lock icons that you can toggle to lock different properties (like $Z$ scale).