It's good to keep in mind that the test simply measures your natural tendencies along a spectrum. The best way I can explain this is that even though I consider my right hand to be dominant, it doesn't mean I never use my left hand.

How strongly one is extroverted or introverted can make for a very different experience even among people who are classified with the same 4 letters. Therefore, it's not necessary that you must fit in just because 13% of the population has a similar personality to you.

To those who fall on the "borderline" of a certain trait, this may indicate you don't have a strong preference for either J or P. Perhaps at work you are very organized with paperwork (J), but when it comes to taking a vacations, you don't care where you go or what you do - it's all spontaneous (P). The MBTI tests themselves are made so that they measure what % of questions you answered with a typical J or P response, but often scores can vary depending on which hypothetical setting you are thinking of when choosing an answer.

So if you get different scores, that doesn't necessarily mean the test is broken. A lot of the times, there are both great strengths and weaknesses that can be associated with a strong preference type. So sometimes it is good to be able to juggle the best of both worlds.