The differences between J and P are usually quite stark, the most contrasted of the four axes, whereas the differences between E and I are probably the most subtle.
If you're in doubt, look into the
cognitive functions each type uses, and try to narrow it down that way. You should definitely be able to decided between P and J that way, but E/I is more of a discretionary thing, I guess. (the reason being; P/J use completely opposite functions, whereas E/I use the exact same functions in a slightly differing order)
(FYI;
being unsure about your type means there's a decent chance you're a P. )