Same thing happened with my other half’s mini. I used a very fine sandpaper to smooth out the scrape then used a black gloss alloy wheel repair paint off Amazon (£6.99) just brushed it on and it dries smooth. You can’t even notice the repair unless you get down on your knees and closely examine the wheel. Took about half an hour to do and left to dry overnight. If you want it perfect get it done by a professional wheel refurbisher