I would suggest that you go for BE CSE in PSG college of Technology.  It would be because PSG is better than SASTRA and also because even after doing B.sc you have to study for masters to land a job. Whereas B.tech is enough to get you a good job. 

Now regarding the CS issue. I would like to tell you that even I didn't studied CS in my class 11 and 12 but I applied for CSE in B.tech during my college and you may feel a little disinterested at first same as for me but with your faculty and peers around , it will come around for you. CS has a lot of scope in the market and I would suggest that you pursue it.