If you are getting low marks, then you won't be able to get admission in a reputed college. But, don't think all other colleges are of low level. In my opinion, it doesn't matter where you are, you have to give your best. You mentioned that you were good in studies. What happened to you is that you lost your track due to some reasons. And it happened. So, leave it. Whatever gone is gone. You have to leave it behind and work for the future. You have your CET on 5th May, and there is about 20 days. So, give your best shot. Prepare well for that. You can score good in it. And, who knows, any of those Mumbai University colleges will be a turning point in your life. Wherever you are, if you work hard, you'll get good results.

And, if you score 75% or above, then you can drop this year and prepare very well for a year and crack JEE 2019.

Dear Tushar, 

You can apply for entrance exams conducted by different states like Karnataka, Andhra Pradesh. Karnataka has Kcet and Comed-K similarly Andhra Pradesh conducts its own entrance. 

You can also try for competitive exams for defence services after 12th with a better preparation. 

Good luck.