Just put that leather conditioner on it that you have from the Chemical Guys and rub real hard. You have to rub on it! It should buff right out. It looks to be a minor scuff? I am fairly certain it will rub off easily. Glad it's on the back of the bag. However, that little scuff is very minor and won't be seen while carrying at all, even if it won't come out completely, but I am pretty sure it will, or at the very least, be an improvement.
You have to expect to see SOME evidence of the bag being used, since you bought it used and saved yourself almost $700.00!! If the bag was perfect, she could have easily sold it it for 500.00! If anyone comes up to you with a magnifying glass to look for that little scuff, just bop them in the head with the bag and tell them to "Get outta here" lol! If it doesn't rub off as well as you would like it to, you can always take it to a shoe repair store. They can easily fix it for very little expense. And then right after you do that, you will probably put a few scuffs of your own, on it anyway! lol!
That little nick at the top of the scuff, looks like it got scratched with something sharp, and that's why you can feel it.
It looks like that last pic is a stitch to hold a pleat in place, which adds style to the bag. My God! That bag is GORGEOUS!! Scuff and all! Doesn't take ANYTHING away from that gorgeous bag. You did good, Smiley. I just love all that detailed contrast white stitching. Such a beautiful bag that I am SURE you will get loads of compliments on.