Zarurui nahi k damage ho....but Chances are that overfilling engine oil might damage seals.
To be on the safer side, go back to your mechanic and drain out the oil totally and refill it with 300ml less this time. Just make sure the container in which your mechanic catches oil should be clean. He will charge you 2 or 3 hundred ruppees, but it will give you peace of mind.
i mistakenly overfilled my 1000cc vitz engine with similar volume of extra engine oil as you did. Driven it for 5000 km without any problem. However, its not good to take this risk.
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I was maintaining it from honda for 30k km. But as far as honda oil is concern they use total fully synthetic 5w30 and their rexommended oil change is 5k km. But honda oil seems to be totally worn out at 5000 km.
the more worn out/dirty the oil looks...the cleaner the engine will be. Oil's job is to clean the engine by removing the pollutants off engine's interior. In short, that means that your engine oil is doing its job perfectly.