i have scored 135 marks in jee mains 2020.is that a good score

Hey there hope you're doing well.
Dear aspirant, see score really doesn't matter now all that matters is your percentile score. It's the relative score. May be that the paper was very easy and other people scored much higher that you so although you may be far ahead of qualifying marks your percentile may drop which would heavily affect your AIR. similarly if the paper was quite tough and say people hardly scored 160 or 170 then you would probably placed in top percentile giving you a good AIR. So we just can't judge that your score is good or not. Go and check your percentile 8at official website of NTA. once you know your percentile you can calculate your rank by the formula
(100- your percentile)*869010/100.
Thank you hope this helps you!