Scaling a shape horizontally and not vertically?

i want create simple movie clip of preloader progress bar. create graphic symbol of rectangle , drag rectangle onto first frame of movie clip. add keyframe on frame 30 , use transform tool scale horizontally right. add motion tween make grow.

1. bar grows, however, growing vertically result of tween. how can make stretch right without growing vertically?

thanks!!!

instead of using tween , keyframes scale bar, simple make bar it's full final size, , use _xscale property control scaling find percentage of loaded clip , using _xscale parameter. following:

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