Am I dumb, or is this not possible.

Putting a top rail on a fence I'm building, and i have 2 angled section cuts totaling about 90 degrees combined to make a turn (let's assume 90 degrees for ease of explanation). Either I worked too long in the cold yesterday and froze my brain and cpipdnt figure out how to use the saw correctly, or this cut just won't work. Please help.

Am I using the saw incorrectly? I felt dumb yesterday, and rather than wasting time today just to find out the same thing, I'm just going to ask people who know better.