I've found that sharing while using C3's preview with my laptop's browser doesn't work - mostly because I don't have any social programs installed so Windows just pops up some odd gray screen. Try C3's remote view and test it with your phone.
The image of the code below is from a Wordle clone I built. I have it setup so it takes a screenshot then posts it to social media, it works well, but again, only on a phone or tablet where social media programs are installed.
Hope it helps.