Unless you're doing some super intense work, that doesn't sound normal. I would charge it to 100% and then let it drain down to zero. Make sure to keep track of what you're doing and how long the battery lasts.
Afterward, charge your computer to 100% and leave it plugged in for an additional 2 hours. If, after all of that, your battery does not last 3 hours doing small tasks (e.g. surfing the web, word processing, etc.) then I would have Apple check it out.
Also, make sure to disable unnecessary background processes (e.g. bluetooth). If you're really concerned, it's never a bad idea to call Apple Care.
Hope things work out!