It would be better if you can appear SX stream of KVPY while in class 12 because if you qualify you can avail the scholarship right from the first year of your BSc. Apart from that KVPY scholars are eligible for admission to IISER, the integrated BS-Research programme at IISc. You would also be eligible for admission to the CND programme ( B.Tech in CS and MS by Research in Computational Natural Sciences) at IIIT Hyderabad.

Instead of joining a BSc in any other college and then attempting KVPY SB stream try to prepare well and qualify the SX stream to give you better options.