That mark is normal. It won't get any worse.
I just pulled mine apart again...just put some talon grips on it...my barrel has a very very tiny wear mark there...almost cannot see it...have 500 rounds through it
I cleaned my 2 320's yesterday , they both have a slight wear mark as you have described. One gun over 3k and the other 500 rounds.
There is no burr .
They are both accurate.