At the edge of the atmolayer you are looking down at a circle.
Except the curve at circa 24 km is the same in Australia and Denmark, as I've previously shown here on the forum with my own balloon launches. Do me a favor and locate Copenhagen, Denmark and and Ballarat, Australia on your bipolar flat earth map and answer the following:
Are Copenhagen, Denmark and Ballarat, Australia (near Melbourne) equally close to the outer rim in your opinion?
If yes, then neither the accepted flat earth map nor the globe map are close to being correct. If no, then answer me why you observe the same degree of curvature at equal altitudes both in Australia and Denmark.
The balloon pops simply because the pressure inside it gets too high.