At 02:41 She says
It's just that I'm an artist
this is not what I'm supposed to be doing
What does that mean?
I didn't watch the film, but "it's just that ...." is often used to introduce the reason for some discontent, issue, trouble, or concern. "It" refers to the situation that is the basis for the feeling.
Why are you looking at me in that way?
--It's just that you are eating my sandwich. That one with the cheese is yours.
You seem unhappy here.
-- It's just that I love the outdoors. I shouldn't be working in an office.