I can understand your annoyance, eternity, but I am sure that Fr Tim was in no way annoyed with you - if you were arguing, quite the opposite! It is often difficult to address a complex theological topic in a single lesson, especially when that lesson is meant to engage the whole class. But the point you raise is both valid and current, and thus fascinating....
The historical teaching of the Church is simply this:
Extra Ecclesiam nulla salus that is, "Outside the Church there is no salvation". Pretty black and white, huh? Well, not really. The teaching of the Church is clear - if anyone is saved (finds themselves in heaven) then it is through Jesus Christ and him alone. However, because God is merciful and gracious it may be that some people who are not "card carrying Catholics" will be saved. And that is certainly something that Catholics should hope for.
The salvation is non-Catholics is therefore not-excluded, though in some mystical sense even they will be saved through Christ. After all, Christ loves us with a love we cannot even manage to understand. We often make a mistake about the dynamic of belief and salvation - it is God who pursues us, not the other way around!
To put it another way - our faith in the Catholic Church may be great, but our faith in the Redeeming God is greater.
Does that make sense?
Sacerdos