_yscale help

why does this only make the x scale change and how can i get it to happen when the mouse is on the clip rather than when it is moved around on the clip?

onClipEvent(mouseMove){
if (this.hitTest(_root._xmouse, _root._ymouse, true)) {

onFrameEnter()
{
this._xscale+=(120-_xscale)/5;
this._yscale+=(120-_yscale)/5;
}
}
else

this._xscale=100;
this._yscale=100;

}