Dear AW: commit to the role or get off the stage!
Girls Season 1: Ok, you had a 'sex' scene with Charlie in his bedroom while completely covered up with some sort of "tank top dress" where no skin is visible. It was your first time at this dance, so I cut you some slack (while cheering Lena Dunham for going balls-to-the-wall with her nudity even though she's no supermodel . . . not even a Lane Bryant supermodel).
Girls Season 2: Another, more ambitious 'sex' scene with Elijah, and you tip-toe closer to the edge of the nudity pool, but fail to dip your toes in the water, let alone dive into the deep end. Allison, real women take their panties off before sex (instead of hoping that the pulled-to-the-side thong strap isn't going to interfere with the motion of the gentleman's ding-dong). But the more egregious sin was folding your arms diagonally across your bosom during sex (as if you're a corpse laid out in a casket). Real women don't do that, either.
You're a gorgeous girl, but your naughty bits aren't made of gold. They (like the rest of you) won't be gorgeous forever, so stop treating them like they should be vaulted in Fort Knox and let them out to breath free air now! . . . not later when you want to proclaim "I've still got it" by posing for Playboy when you're 50!
I'm not saying all this because I'm a dirty old man who wants to see your junk. I can go down to the local strip club and see all the prime female naked-osity I want. That's not the point.
The point is that your timidity is a form of "breaking the fourth wall". You're killing the reality of these scenes by telegraphing to the audience that you know there's a camera there and a million viewers on the other side of it . . . and that kills our ability to suspend our disbelief.
Seriously, you're a fine actress, a surprisingly good singer, and an absolutely stunning beauty. But if you can not -- or will not -- do the nudity that a role calls for, then please pass on it and let someone less prudish take it, while you pursue other acting jobs that don't call for disrobing.
I don't get your hang-up (if Kathy Bates can go full-frontal in About Schmidt, what excuse do you have?), but then, I don't walk in your shoes. Nevertheless, at the end of the day, there comes a time when you must realize your limitations, and either break on through to a higher level or learn to live within them, and that time is NOW for you and the things you will or won't do as an actress to help tell a story.