I find that new bras often need a few wears to become comfy. In addition, if you've had a fairly drastic change inb size, the bra will be sitting on areas of skin that are not used to having anything sat there. Give it a bit of time.
I often have a few 'scoops' throughout the day to make sure everything is still were it should be. If the band starts to feel uncomfortable, I find that a quick scoop sorts it out!