wrecked cylinder???

my cylinder keeps on scuffing up each time i rebuild it, the petrol and everything is fine and scuffs up worse everytime. my question is when i look at the cylinder there are two scuff marks, black going straight up from the middle induction port about an inche long. Is my cylinder out off round? can i keep on riding it for a bit longer, it runs fine and has heaps of compresion?
thanks for any help.

also where the scuff marks are you cannot see any hone marks, they are about half an inche wide