dubbadhar issue on 7 inch screen

Hello community,

I was hesitate to post in Pi section or in themes as it is clearly linked.

On my Raspberry PI3 with Kuman 7 inch screen, donuts are “ovals” instead of “round”

Screen ratio seems altered. I've test on my local browser on my computer and of course, rendering is perfect.

I've try to reinstall my Pi by letting automatic and trying to select some settings with 1024x600 but still not perfect.

My model is https://www.amazon.fr/gp/product/B07LF1GYXS/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

Any trick to get perfect monitoring screen ? 

Cheers