1. did you look at my post, “Rear ventilated 300mm disk”, 2. in your photo it looks like one of the pads is in backwards? Also are those AMG calipers with a sensor? The SRT and NA do not have rear wear sensors, the #1 photo on my rear 300mm upgrade for a NA shows the caliper you need. If you got the SLK 3.2 AMG rear calipers I do not know if they will go on the Crossfires.
what year and type car are you doing this on? Even tight pads will not score a disk like that.
It looks like the calliper is too close to the rotor spacer are probably required, the photo shows the pad right inside the calliper, if the pad on the other side is well out of the calliper surely a spacer of the correct thickness to equal the pads out.
Maybe it the wrong combination of parts.