You don't know how to define yourself because human psychology is more complex than a simple A/B choice like introvert/extrovert. Even something like gender, which you think would be cut-and-dried due to clear physiological differences, has complexities. Something as vague as 'how do I generally behave in the presence of others' doesn't stand a chance.

Introvert and extrovert are fine as loose labels, but they're really not suitable to be used as actionable terms.