I was designing a hexagon-based logo recently and came to horrid realisation: 6-sided polygon in Figma IS NOT a perfect hexagon, where all sides should be equal and angles 120 degrees. Everything is slightly off.
Take a look: black line is a perfect hexagon and the grey one is a default 6-sided shape from Figma
Where did you get this hexagon from? Here is a freshly-created hexagon in Figma I just made. I put the lines on manually for measurement. As you can see the angle is perfect (slightly off because of manual placement of the line) and the two lines are exactly the same size. Maybe you didn’t hold Shift while creating or resizing the polygon?