Your interview went good...you were confident in explaining everything you explained everything fully....i think you should be confident about the result.

As far as early jitters were concerned look everyone's heart is racing before one sits on the chair... But that's why they say "make yourself comfortable" because as soon as you sit down it becomes a conversation and the person doesn't even realises how quickly time passes......

I disagree with the fact that interview carries 30% weight age... I think alot depends on your interview....

So best of luck for this and IB as well....