Richard
While I feel your pain, it is very unlikely that such a small mark will have serious effect on the images. Wait until you actually use it before getting too depressed!!
Major question that comes to mind is what is the dust cap made of? Obviously a metal one is going to have a greater effect than a plastic one.
BTW, I note you are an archer (lot's of 'em on IIS) I did archery for many years, what do you shoot?
Malcolm