Im working on a project, and my first clip previews fine in the top left window but when i play the preview of the whole project*(in the top right window) the first clip has a bit black box around the main content of my video?
does anyone know why this is or how i can get rid of it?
From your description, it sounds like you are first referring to the Source Monitor, which just plays the Clip, irrespective of the Sequence/Project where it will be used. Then, you are referring to the Program Monitor, which plays the Clip(s) IN the chosen Sequence.
You have a mis-match between the Sequence's Frame Size, and that of your Clip. What is the pixel x pixel Frame Size of the Clip? What is the Frame Size of the Sequence? Also, please list the PAR (Pixel Aspect Ratio) for both. Based on your stated observation, I will venture that they do not match.
Joe's suggestion should fill the Frame (depending on the height and width of the Clip in pixels), but you might need to do some manual Motion>Scale, and effectively crop that Clip - it just depends on the exact mis-match.