I'll send you some Sympathy, (you got your 300 around the same time as mine) but I agree with the above.
I would take the seat out like you did and there are plenty of products to clean leather. Leather seats are really very durable and being black, I would think you could get the spot to not show.
Honestly, I love the smell of most new cars but the 300 really has a smell of electronics and other man made stuff as much as anything.
I use Zaino leather cleaner on my other cars and not only does it clean and condition, it makes the cars smell what I really think a new car should smell like.
You'll get thru it Bro! Like the others, I have done worse...
Some sympathy for you Bro: