Matte gets distorted after applying effect

Hi!  Wishing you all  a Merry Christmas! 

I am making an infographic.

So I want an wave to appear inside a box. once the box finishes its animation the wave will appear inside it.

so I draw an wave shape, applied set matt so that it only appears inside the rectangle/box. All was okay so far. but once I apply wave warp on it it comes out from the container(rectangle/box).

I want it to stay inside like it was before the wave warp was applied and then it will move inside, not outside.

Why is this happening?   😥

Please help 😥