Will using the elliptical at high intensity cause me to become thinner? (I don't want that, because I am already thin).?

I am a slim woman and I want to get into toning.
I already do 40 minutes of the elliptical on low intensity (although I know I can do far more).

I want stay my weight, which is 120-125 lbs.
But I want to tone and build a little bit of muscle?

Will doing the elliptical at high intensity cause me to build muscle? or cause me to become even skinnier than I am?
Will using the elliptical at high intensity cause me to become thinner? (I don't want that, because I am already thin).?
Post Opinion