I say "if".. Not because what people think, but because how it is like. But I wouldn't call myself negative.
I think, not taking it for granted and worrying a little that you might fail, would give you even more positive energy at the viva. Being a nervous and worrying that you might not pass can be a positive thing, it shows that you take it serious and you are aware of the consequences.
fluffymonster will tell us on Monday if the approach of "if" is good, won't you fluffymonster .