You can bodydrag quite some upwind indeed
Your error, without having seen it, I am quite certain though, is you point too high with your arm/body, thus you are getting nowhere upwind...
A common mistake by almost everyone, even quite experienced kitesurfers are seen doing it somewhat wrong, only helped by the fact the wind pushes their board down to them most often...
You should make your "superman" with your body and arm perpendicular to the wind, instead of trying to partly point up to your board.
Sound counterintuitive yes, but try it, and you will see how much better you go upwind, eventhough you at first feel like you must go sideways
Made this many years ago, a test where I ditched the board on purpose and then bodydragged with my 10 m2 kite to see the result on my GPS after the session, quite amazing angle I would think: