If you didn't, it's not the end of the world.....COVER immediately first thing Monday morning and lick your wounds and move on. There may be a bidding war, so there is possibly alot more pain to be felt.
I caution all shorts or potential shorts to rethink their positions. It is not a "us" (longs) versus "them" (shorts). I live in a world where I hope all can win or in this case benefit financially. I would not short this stock predicated on the real possibility of a take over. If you want to short, focus on companies whose fundamentals are eroding or are just over prices. Some examples that come to mind quickly are FIT, AMZN, NFLX.
For disclosure purposes, I currently have a long position in HUM.