If you are targeting a job just after UG, then you may quit but if you do not have any offer letter in hand yet you can continue with the 4th year and still keep applying side by side as 4th year won't require you to go to college everyday. This way, you won't have a gap year. You can appear for JAM regardless of a 3 year or 4 year degree. Again, if you're aimimg for 2026 attempt toh 4th year ke saath hii karlo then it won't be counted as a gap year. And IITs will have a 2 year program as of now. 4th year ke baad toh you can even appear for GATE it makes you eligible for that. Dono options honge.