Trim path working weirdly ?

Hi !

I am new on after effect. I am trying to create a simple animation of a loading bar. I've watched a handful of tutorials and they all manage to do it in a few clicks. But even when I do exactly like them, something is wrong with mine. I created a rectangle shape and used trim path to slowly make it appear, from left to right, just like in the videos. But mine will start from the right and fill up weirdly ( see the picture ).
Does anyone have an idea why it's doing that ?

Thanks in advance.