You have a great eye for form. The proportions are pretty solid overall. I'm impressed, considering you've only done 5 so far.
Just keep pluggin away and practicing. Gesture drawing NEVER fails!
Don't be afraid of Shading. Adding shadows will help complete the shapes you're seeing, often more so than a sharp line will.
Also, there's no reason to be bashful about nude art. We're all adults here. ;P
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