This is a fairly common problem that won't effect the way you Nexstar flies. I'm a newby also and I have similar marks on my spinner. The marks come from not having the starter cone pushed onto the spinner hard enough when starting. Try pushing just a little harder on the starter when you are starting your engine and the problem should not get any worse. You can change the spinner if you want the Nexstar to look better, but it isn'e necessary. Now when I start my Alpha 40, or my Pulse I grab a place on the plane where I won't do any damage and where my body is clear and I push the plane forward just little so the started and spinner fit tightly together. This keeps this problem from happening and makes starting easier.
Indy Park Flyer
Hangar:
Hangar 9 Alpha 40
Hangar 9 Pulse XT