Introvert or Extrovert - neither is right nor wrong. You cannot change the fact that you are an introvert or extrovert any more than you can change the color of your eyes. So embrace who you are and make no apologies!
This guy gets me. There's a a point in time when you reach a certain age when you just feel like not having plans sounds 100 times better than going out. For me this feeling hit at age 18. And I have no shame in it.