Mc resize problem

hi guys

I have been searching the forums for an answer to my problems, no joy though.

I have a mc on the stage, my stage is aligned to the bottom but im trying to align the mc to the top and strecth from left to right fullscreen.

Im using this

 my_mc._width = Stage.width 

but this is not working properly?

My flash movie is set to 100% with no stage scale.
Thanks for help