Hannah is comfortable with how uncomfortable she is with her body, just like she's happy to be open about her limited romantic and sexual background -- her abrupt honesty is a way of deflecting from her own inexperience, a means of being up front in order to actually pull attention away from larger insecurities.
In a scene in the third episode that's more difficult to watch than any of the awkward sex, Adam jiggles Hannah's belly until she squirms away, laughing "This is so horrible!" and covering herself up. He suggests indifferently that she lose a few pounds if it bothers her so much, and she whirls on him to affirm that it doesn't, that she has other priorities, just how much she does care openly warring with her need to not be the kind of chick who gets dragged down by body image issues.
And nowhere in the show does that come through more than in the bedroom scenes, in the sight of sex-positive and totally open but actually pretty inexperienced Hannah bravely heading out in black eyeliner, a miniskirt and teased hair in pursuit of some Carrie Bradshaw adventures, and getting her heart and her self-esteem a little trampled by the reality of what she experiences.
That's part of life, too, especially in those uncertain years right after college, and it shouldn't be shot down out of a misguided sense that the young women on screen or those watching it need to be protected. Aspirational fantasies have their place, but so do the failures, blunders and embarrassments that are part of growing up -- how people learn and move on is just as important as how they succeed.