l sometimes put the ball of my foot on the pegs, or right in the middle of my foot.What is correct?

Riding on the ball of your feet and in the middle are both correct. Its all just up to which is more comfortable to you! l prefer riding on the balls of my feet. It allows me to bend easier and my feet dont slip off of the pegs as easy.

it really is up to you and wat is comftable for ya...i move my feet around alot especially when cornering..but l find the balls of my feet the best for me it stops slipage

Individual preference! Each person has their own idea of what is best and what works for them. If you are too far on the tips of your feet it makes it too hard to change gears.

it depends on what feels comfortable for you. l like to ride on the balls of my feet when l know l dont have to shift or brake for long periods of time.(i am a desert racer) .
but riding on the arch is also more comfortable...
there is no cut and dry one correct way to do it, do what feels comfortable to you and ride....