The first condition to get admission to any top B-school (Top 25) in India is to do well in the written exam (which is the first round of the selection process). Profile, which includes your academic record, extra -curricular achievements, work -ex etc, is only one of the parameter which goes in to the consideration during the admission process of a good B-school. .
Having a below par profile is certainly disadvantageous but you can compensate for this disadvantage by doing well in the written round. Some colleges consider the profile as an input to give the GD/PI calls (which is the second round of the selection process) and most of the colleges consider the profile only during the final selection (i.e. after the second round). That means that for the majority of the good colleges you can further compensate for your weak profile by doing well in the GD/PI round. So, there is plenty of scope. Secondly, if you know that your profile is not good then you can start working to make it good; yes this is difficult but not impossible. To achieve this difficult task, rather than making one big effort, you have to make the small iota efforts in many directions. For example, if you have never scored 80% in your academic life, expecting from yourself a score 90% in next semester is unrealistic. But you can certainly aim for scoring 5% more than your usual score, you can look to participate in the state/national level events, you can start taking leadership positions, you can do meaningful internships and perhaps many such small things. The many iotas will help you 🙂
Remember, your past efforts are affecting your present, that way your present efforts will also affect your future. Past cannot be changed, but future can certainly be channelized. You should focus on improving your profile and put efforts to that effect.
Now, for the admissions to the good B-school. You may not get a second round call from few IIMs who take profile as an input to give the calls for the GD/PI round. But you will certainly get the calls from the other IIMs and the top B schools, provided you score well in the written exam.
Bottomline is this: Do not think about the obstacles, prepare well, live with the drawbacks and build strengths to overcome the drawbacks.