The camera width looks narrow and deforms when use a screen that is configurated in vertical mode.
I wonder - do you happen to have a picture of what you are experiencing? It would be great to know what devices you are testing with.
It would also be good to know if you have tried our Bootstrap examples and whether you get the same results: https://docs.zap.works/universal-ar/web-libraries/a-frame/bootstrap-projects/.
All the best,