Ahhh its good to see another Hakuryuu cosplayer!
What I did is reallyyyy simple. After putting on foundation i put an extra layer on the side of the scar. If you have red masscara or something (hell red lip balm worked too haha) dab it on the scar side. You don't have to completely block your face out with red but make sure you've put enough for however big you want it. Use black and brown eyeliner and do curved strokes on over the red blotches but dont over do it (it'll look really shit but dont worry haha). After with foundation, blend it. Again don't over do it but get it to the shade you want it to be. You can add a bit more afterwards if you need more colour to it etc.
This is how mine turned out:
Its a really simple way haha but I was happy with how this turned out ^^