You're not looking at a large enough percentage of the planet's surface to actually see the curve. You're simply not high enough and the terrain itself is masking it.
This is over 1,000 feet up, looking more than 20 miles away. No curve:
~35,000 feet over Georgian Bay, no curve
40,000 feet over Winnipeg. Maybe there's a curve?
It's very subtle even from an airplane so don't be upset if you don't see it from ground level.
500 feet up, hard to tell if there is a curve because the photo is so grainy
120 feet up. Curve??
Anyway back on topic, I don't know why I didn't post there here yet: Toronto's skyline as seen from the 7th floor of the Sheraton Hotel in Hamilton:
All photos are mine