U may get admission into IIST. But there are some points to think also before u join IIST.

First the Bond for 5 years, (breaking which will cost 10lacks) which means u can't pursue furhter studies like MS etc as they may not give the reco letters as well  and u have to serve ISRO for 5 years.

Second the salary is very  low by the present standards. The private companies are paying high whereas the ISRO salary is too low.