this shouldn't be any problem since Solid Edge is able to develope any surface to a flat pattern since ST7
You have to be within a part and finally You need to be in ordered mode.
Then go to extras where You also will find the flat model and here the second option (other than sheet metal flat pattern) the "platine body"
here you can select any surface or group of surface for which SE will create You the flat pattern of it
What is this "Extras" tab? Is this something that SE Premium has?
Edit: Nevermind. It's "Tools"
So what I get when I use the "flatten" tool is something that looks like this
Not sure why I can't get it lay completely flat.
could it be, that You have selected the wrong developable surface?
For me the picture looks like You have selected the side surface instead of the top surface.
You have to use those surface which should be flat afterwards.
Not the side surface You want to cut then as laser cut.
So here is the part I have modeled in my pictures. We want to cut these on a CNC table, using the widest face as the flat surface. If you look at the other faces, then you can see why we want to do that.
I have some other examples of triangular shapes, that we would like to cut too.