I've been having a faff about again today, this is what I was trying to do a few days ago when it all went horribly wrong.
The shot of Hull marina wasn't the best to work with as each side of the original was difficult to blend. In the end I resorted to patching out some of the boats, its far from perfect but I am now beginning to understand how some of the editing tools work
I'm sure you've seen these many times before but this is the excellent tutorial I followed should you be interested https://www.youtube.com/watch?v=j06DahjMQq0