Hold on to it and if the price keeps dropping buy some more if you can afford it. I bought my first at €800 and then the price dropped to around €300. Bummer, but I bought some more and when the price went back up to €500 I would have been able to make a small profit by selling them. I haven't sold any BTC yet. I thought I was late to the party in 2013.

In the mean time, make sure your 1 BTC is secure in a desktop wallet, read the manual of your wallet, know how to backup and restore your wallet. Seeing the price drop is bad, losing your BTC because of a computer crash or virus or because the exchange gets hacked is the worst.