Need help to finish my McLaren Senna MSO Carbon Edition

Hi everybody,
So as I said in the title I’m workon a very special Senna but I have some issues concerning the painting…
I want to paint the interior of the back fender but when I dit it, the color is applied on the exterior too…
So is it possible to paint only the interior ??
https://image.noelshack.com/fichiers/2019/25/2/1560861977-senna-ailes.png

And I want to do something similar but on the front fender. As you can see I want to paint the interior of the left fender then I had to go through the right fender but the colour is being applied on the two fenders.
One more time is it possible to paint only the interior or no ?

Thanks you for the consideration, have a good ride and I hope I will finish this beautiful car for you one day :smiley:
XOXO

No the paint just goes through them all.