Very nice sketch. I really like the almost realistic-anime style of it. What might make her seem 'mannish' could possibly be her cheekbones. Her jawline seems a bit square. In anime, generally female characters have very pointy chins, and the curve down starts just under the eyes. Here, she has actual realistic cheekbones and cheeks. I think if you made that line less curvy and more angular, it might eliminate the 'manliness' you are seeing.
Personally, though, I think she looks fine. But that was the only thing I could point out that might be causing the problem you mentioned!
It is pretty good too me. She doesn't look man-ish. Keep it up! :)