First make sure the fetish (bird carving) is centered on the rectangular hole in front of it. The hole should not be covered by any part of the bird. The bird should be just at the edge of the hole or back a bit (1/32″). Be certain that the bird is tied down snugly. Then hold the flute up to a light and see if you see any light between the bird bottom and the flute.
The longer the bore is on a flute, the more challenging it is to play. The reason is that the air has to travel farther and it starts to diminish its power. So the natural reaction is to blow harder which in turn creates an over blow on the sound hole causing it get breathy. In fact, the longer bore flutes do need to be played more subtly.
We make our flutes a little bit differently from other flute makers allowing more air to be blown into the instrument without the bottom note breaking to the high octave. The down side of that is that it can sound breathy when blown too hard.
This is typically resolved through experimentation, by varying the breath and backing off a bit.