calorie loss per day?

I've been wearing my heart rate moniter all day (the FT7), and from what it tells me, my typical activity (walking to class, standing, cooking, just my regular routine, I didn't use it for gym activity) runs me around 400 calories per two hours. My average heart rate was 100bpm exactly. so... minus 8 hours of sleep, I burn 3,200 calories a day by just existing?! that can't be right. I figured by wearing it all day I could get a more accurate level on how many calories I should be eating a day but. I can't possibly need 3,000 calories to maintain my existance (I'm 5'3 and 155lbs and female btw). help?!