Need Help with Scrolling Menu (runs off stage)

programming flash
1

Can someone please help. This scrolling menu runs off the page and I don’t know how to keep it in the boundaries of the stage. Any suggestions? I’ll take anything. thank you!

** Here is the AS and I have attached the file below!
**
var myShape:Shape = new Shape()
myShape.graphics.beginFill(0x7E00E3);
myShape.graphics.drawRect(50,10,450, 100)

addChild(myShape)
menu_mc.mask=myShape

stage.addEventListener(Event.ENTER_FRAME, movemenu);
function movemenu(myevent:Event):void {
menu_mc.x = menu_mc.x + (0.5 * myShape.width - mouseX) / 40;
}