The things you speak of aren't fitting in so much as basic life skills many of us take for granted. Even those who pretend to have it together don't always.
Says the woman who woke up to 26 cents in her chequing account.
They will come with time. It isn't so much inauthentic as perhaps a new skill set that is both challenging and frightening.
To me it would be inauthentic if you paid bills but didn't believe we should. Or hated grocery stores but shopped there, kinda like me and Walmart. (how they can sell Tide so much cheaper than anyone else)
You have to remember, growth comes from stepping outside your comfort zone. As a teen I was horribly shy, I started public speaking competitions. I did pretty well, in my 20s I sank back into my anxious, shy shell until, for work I was forced out. Man I felt like someone else. Now I speak frequently to large groups, you need a hook to get me off stage. I give talks, lead round tables, participate in and facilitate pitch competitions. I made enough pitching to cover the expenses of one of my companies until it turned a profit. At first it seemed impossible, i thought who am i becoming. Now it is so natural, I do it without thinking and it is absolutely who I am and completely authentic.