I don't think it ever helps things to pretend to be what you aren't or pretend to believe something you don't.

You can't do a whole lot about what your friends believe (that you'll go to Hell) and though it's nice that you care about them, I would just tell them, if they are pressing on you (a boundary violation) that you are not interested in discussing your beliefs at that time and tell them that they're your beliefs and just as valid as their own and you don't believe "arguing" is going to change anyone's mind.

It's generally not real polite to bring up and talk about religion, money or sex :-) with people you don't know very well as a lot of people do get upset or do not wish to talk about their personal feelings or beliefs so, if they're mentioned I just don't enter the conversation and if it gets too uncomfortable, strident or something, I would just leave.