but I have got only 55% in HSC and 41% in PCM .....what sholud I do 

No as such to get admission in private college, not a very high score is required but then it varies from college to college. But still a score of 75% or above is respectable as well as enough to get admission and moreover you should also focus on getting marks above 65% in PCM each. With this score you will be on a much safer side.
Best of luck!!