Nikola is strictly all masculine to me, which is why i've always cringed when hearing it on a girl. Silly people think that it's 'feminine' sounding when in actual fact it isn't. There are feminine versions of it and I guess non-name nerds have no clue how names work.
I say go for it :) No doubt some people will think of it as 'girly' but what would they know! I'm not a huge fan of it, but I see the appeal. It's strong and slightly delicate at the same time, which I think adds to it's appeal.