Makes you dredge up some high school Geometry doesn’t it?
Here’s the manual way I used earlier. I used the same method for yours with the added step of the center hole.
You need the length of the side of the cone from the apex to the edge. 9.9 in your model. You also need the circumference at the bottom edge which you can get from Entity Info. 34.6 in your model.
I drew a circle with a radius of 9.9 and the circle for the hole at 2.7 to match your truncated cone’s lower and upper circles. Then I got the circumference of the larger circle (62.2) and did the following math.
34.6 / 62.2 = 0.556
360 x 0.556 = 200.26
Then I used the Protractor tool to place a guideline at 200.26° from the starting point. (the line at the 3:00 o’clock position on the center circle.) I made a component of this geometry so the next geometry wouldn’t stick to it. Next I used the Arc tool (not 2-Point Arc) to draw arc with 24 segments through 200.26° at the two radii and I connected their ends to get the face which I moved over to the right. For my first example the only difference is there’s no need for the smaller circle.
Note I used 24 sides for my circles and the arcs because that’s what you used. I would match things up with whatever number of sides you used when you made the cone.
Here you can see the segments of the edge of the 3D cone and the flat pattern match as one would hope.
FWIW, since SketchUp recognizes the circles and arcs as true circles and arcs for circumference calculations, this method, though involving some math is likely to be more accurate than pulling a triangle or trapezoid out of the model and copying it. It also means that you can lay the pattern out more easily with basic tools. No need to print a full size pattern or anything.