I create a new video track, i imported my picture, then i drag my picture onto the audio track, but the picture is stuck in some sort of "invisible wall" and i cannot move it outside of the "invisible wall". And this invisible wall is a very small compared to my video. Here's a picture
This is happening because the aspect ratio of your picture does not match the aspect ratio of the project. Open Pan/Crop on your picture and right-click on the window and select Match Output Aspect. Then resize the Pan/Crop to make your picture the correct size. It should no longer get cut off.
You could also use Track Motion to position the picture on the screen anywhere you want. Be sure to use the correct tool for the behavior you want.