I found this interesting, so I created a 360° panorama - now you can see precisely how the photo fits in context.
https://kuula.co/post/792h3The red line is your eye level - a plane, viewed from in the plane. It will always appear as a straight line.
The purple line is your sea-level horizon, at 2.9° below eye level (as calculated with Walter Bislin's earth curvature calculator,
http://walter.bislins.ch/bloge/index.asp?page=Advanced+Earth+Curvature+Calculator).
Note that the purple line is the edge of a planar circle. You can see the curvature of the edge because you are not in the plane - you are looking down at it from above.