Can someone point me to a resource to explain whats going on with the camera?

I cant figure out why the preview and the play are different. Ive tried all sorts of things to keep them the same, dynamically calculating fov, attempting to adjust the distances, changing the position. I am out of ideas and I don’t even understand what the problem is hence the try it all and see if something sticks. Anyone have an idea and can point me to a tutorial or resource or… anything that will send me in the right direction?