There is a danger with MBTI or any other personality/temperament identification system to pigeonhole people and ultimately to oversimplify the human mind. As I said earlier, I think I have a strong rationalist inside of me, as I tend to look at situations in a scientific manner, but that doesn't necessarily make me an INTP. Ultimately typology is a fun hobby for me, although I admit I would very much like to be able to type myself as one concrete type. Ultimately I think it depends on what mood I'm in on any given day of the week.
The MBTI is a starting point for understanding humans, but it shouldn't be accepted as the be-all and end-all of understanding personality, but rather as an entry point into learning more about what makes people think and act a certain way.
Also, you mention being a withdrawn ENFP. That wouldn't be at all unreasonable. I've read ENFPs are the most introverted of all the extroverted types, if that makes any sense. I'm pretty sure my sister is an ENFP. She feeds on her interactions with others and is often the life of a party, but there is a side to her that periodically needs to shut out the world and have solitude to "recharge her batteries"
On the same token, I think INFP/J types, while very much introverted, can occasionally come off as extroverts. We just have to work a little harder at it, and it takes its toll on us much faster than it would on any of the Exxx types.