Inside screen has Red mark

When you turn on your system do you see a full grey screen just before your system finishes its boot up? You also may want to note the location of the display edge (the edge of the grey screen) I'm suspecting you're seeing a bad placement of the cover mask within the LCD. I haven't heard of any issues like yours before for this series. This could have been a parts defect unless you opened your system or damaged it somehow.

If you still have AppleCare coverage I would bring it into an Apple store so they can replace the screen. Even still I think you'll find its cheaper having Apple do this than you doing the repair your self. Ask for the bench rate and the cost of the part then tell us what the estimate is before you OK the repair.