Hello,
Before Making Any descision I would like to bring in your Notice that You can appear for JEE advance two times one in class 12 and second in the following year. If this is your First year in BSc then only You can appear for JEE advance otherwise not.
Similarly You can appear for JEE Main thrice in consecutive years so jut keep in mind this things before you drop BSc.
Even you can also come to IITs after BSc through JAM.