No, you don't really need them in the beginning ... I was throwing up constantly and lost weight, my midwife said it was fine and that my body would catch up eventually.
I don't remember the app saying that, but if you read other sites they say you actually don't need extra cals in the first trimester (just extra nutrients), 200 extra in the second & 300-350 in the third. That's also what my doctor suggests. I'm in my third & there are a ton of days I don't get that many calories, yet our daughter was 4.7lbs at 34wk US (on target, higher percentile). RDI is calculated with a formula taking into your height, current weight & activity level... but the problem is that there are many other factors that may contribute to how much food is right for you. I personally believe eat what feels comfortable, when you feel full stop. I'm not a doctor, I am in the public health field though & have taken quite a few classes on nutrition, so that's where my ideas come from :-)