Naz, you're close but not in my hood....
Would offer up my Paint Meter if you want to try the wetsand route - as the meter will at least give you a gauge to work on.

If it's smooth, it looks like you might need to cut deep to deal with it , which in that case, I would leave it alone. Is there a different area on that car where it has similar stains, where you could afford to *wetsand deeper* to test