My kitchen was remodeled. Down to the studds and the contractor had the plan

There is a small gap between the window casing and the cabinet. The window is over the sink. The whole for the undercabinet lighting was done at the beginning but for some reason, it was not closed until the kitchen was finished. Due to the small gap, the work does not look smooth. The contractor told me that there is nothing he can do to fix it. I am concerned as this is a main focus. Thoughts?