BITS Pilani is a top institute and if you get admission here then it is worth it. But now that you are talking about dropping a year,there are certain factors that you need to consider.
1) Do you believe you have the capacity to study well enough to clear BITSAT?
Since you are considering dropping a year, I assume your results weren’t as good as you had hoped for this year. If you think that you can put in the hard work for a year and remain determined to get admission to BITS Pilani then you can consider dropping a year
2) Are you getting an admission anywhere this year?
If you are getting into any decent college then you should go there and simultaneously try to prepare for BITSAT if joining BITS is really important to you. If not, it’s okay you can focus more for the next year.
3) Be prepared to listen to criticism from friends and family members who will make you feel like you are making a terrible mistake by dropping a year and you should just study wherever you can.
Good luck.