If you have not yet started with your fourth year then you definitely won't have to pay for that. Moreover every college has their own policy but in general if your year hasn't started yet you can easily discontinue without paying for the same. Even if it has started and they have not yet mentioned you to pay then you may not. 

Hello

You have not specified the college or the branch you are currently studying in. As far as I know, only integrated courses such as IMSc and Integrated Mtech offer exit options where you can wish to discontinue after completion of your bachelor's degree course within that course duration. Btech generally does not have an exit option. Please consult with the Head of Department of your respective college department for a detailed answer to your query.