OK, what fuel did you use? Hopefully you ran RTR or basher type with good oil content. Also, see if the marks on the piston and head are just marks that can be cleaned or polished off. If there are small pits in the head and piston, thats most likely detonation or something was in the engine. If the piston still builds compression after it closes the port opening and get stuck in the sleeve before it reached TDC, then it should still be OK to run. That would mean you still have good pinch. Also look for any scratches down the piston that go completely down the skirt. This will kill the compression eventually as it gets worn in, but like I said, if you can clean it off or polish out the marks, then you can at least still run the engine.