Wow! It's pretty rare to have a newborn sleep such long stretches. She's still a newborn, so don't worry about whether her sleeping schedule seem weird. Just put her down when you think she'll sleep. She'll do better and be happier than if you wait until she's overtired. She's not supposed to be on a toddler's sleeping schedule. If you put her down earlier, you might even get to eat dinner in peace! When my little one is overtired and can't get to sleep, I give her a warm bath, or swaddle her and bounce her in a dark room. It also seems to help when there is some ambient noise - the radio works best so far. One thing I noticed with my latest babe (12 wks) is that if she goes to bed earlier, she's up for a short stretch in the late evening (like 9-11pm or so). I don't know when you like to go to bed, but it's something to be aware of. Try to get her down earlier and see how it goes. If it doesn't go well, you can always change it back - very few things are set in stone w/kids!
Most of all, remember that she's still a newborn. It's great that she's sleeping well, but she is not supposed to be on a hard & fast schedule at this point. I would strongly disagree with the poster that recommended Babywise. Whatever "training" method you choose to use (if any), it should not be started until baby is at least 4 months old. Before that, she simply needs to have her wants/needs met immediately.
Best of luck,
S. L