A website claiming to double your bitcoin is just like a street juggler who turns piece of toilet roll into a one dollar bill. Its all scam taking advantage of ones thirst for money and looting them all along. It would not be long enough for all to know that it was a scam too. So better is not to trust anyone who claim to perform a miracle and double your bitcoins. Remember its your money you are putting at such a high risk and at the end of the day it would be you to loose.