For one thing, it probably wasn't completely charged, even though it might have said 100%. Generally, it takes an overnight charge to REALLY reach the 100 % mark. Second, it often takes a day or so for the battery to "settle in". You will find your battery life will get much better over the next few days.
Third, you are probably (as we all do) playing with your new Bionic intensively. Plug it periodically in for the intro period and evaluate the battery life after you have gotten over it's Wow factor.
Also, note that in today's batteries, you don't have to run them down to nothing to get a good charge. They are the next (or next-next) generation batteries that can't be overcharged and don't need to be drained.