go ahead, I actually went from white keys only to black keys only because that's fun
This is your flute melody at 2'29".
First, at bar 5, the melody starts on a sixth and it's a bit clashing.
Then, the musical phrases from bars 1 to 4 and bars 5 to 8 are different in terms of rhythm and melody. This does not give the feeling of having a question and an answer but a long sentence of 8 bars. Especially that bars 3 and 4 give the feeling that the musical phase is finished. So it sounds strange to the ear. It doesn't have a rule, but it would sound better if you took the same thing as bar 1 in bar 5 (either rhythmically or melodically) and put a variation in bar 7 and 8.
This is just an example. It's far from exactly what you should do :)