if earth was a flat disc then.....

A thought occured to me, if the eart truly was a flat disc, surely then, when you see those weather ballons going up(where iadmit everthing looks suspiciously flat, )then wouldnt we see the curve of the penny rather then a straight line? it dosent make sense to see a perfect straight horizin all around, rahter we should see the curve of the flatg dsic

Actually such balloons do see curvature, the horizon is a few degrees below eye level so it curves a bit.  The curve should be expected to be much smaller and much more lopsided on a flat Earth though.

You don't know much about geometry, do you...