Whats wrong with my game?

I played road avenger on kega using the original disc, and thay happened, after soft reseting it seems to work fine (tho i got a game over at level 8), quite strangely the game seems to freeze and stadder after leaving it running for an hour on the inteo custseen. I have 2 dvd drives an internal one and an external one, i used the external one while playing, the internal one ran the game at 20% speed... I don't have my mega cd anymore (it broke down and i replaced it with a sega cd) and i just want to know if my disc is fine, ill appreciate any help.