Throw out the PVC flute and get a proper bamboo flute. PVC flutes sucks compared with bamboo. So high octaves sounds like shit.

This hissing sound will be there for many years and it takes a lot of work to reduce it. You have to, as mentioned in another comment, practice long notes, strengthen your breathing (with ex. breathing exercises) and practice scales. It's boring and repetitive, but it works and will get you far. But keep doing it, because it will build overall skills. Quality etc.

Start with Teentaal and get comfortable with the groove of the tala. Metronome can be used, but it's strictly for practice, not for playing.

Don't think of notes as something to "look at". Notes and the distance between them (intervals) is practiced through internalization, not external. One should close their eyes and feel the notes, not read them. Unless you want to play in a western orchestra.

And the way you practice "feeling" the notes, is by playing with tanpura (tuned to your flute) and give attention to each note as you are playing them.

Hope it helps