Why does my 360 photo look stretched?

The flat file always looks stretched, and that is normal: a 360 photo is usually saved as an equirectangular image, the sphere unrolled into a rectangle twice as wide as it is tall, the way a world map unrolls the globe. The top and bottom edges look stretched, because the point straight up or down is spread across the whole width. In the tour the same photo wraps back into a sphere and looks right.

If it looks stretched inside the tour, check its shape. Panoramr takes a photo whose width divided by its height is between 1.9 and 2.1, and fits one that is not exactly 2:1 to the sphere, so it can look slightly stretched. Export it from your camera's app or stitching program at exactly 2:1, then put it in with Replace Original File on the Panoramas tab. Photo requirements has every rule.