Can you post your part for us to look at?
Not a perfect solution but I have unfolded arc shaped parts by using an arc length dimension and a radius dimension in the sketch. Then create 2 configurations where the folded configuration has the desired arc radius and the unfolded configuration has a gigantically huge radius (R1000, R10,000, etc.) so the arc is almost flat. This technique requires that subsequent features be defined perpendicular to the arc so that when the arc has a large radius (flattened) those features are unfolded also and are positioned correctly.
If you go back into the cut that defined the outside edges of your and tell it to do a "Normal Cut", then you may be able to use the sheet metal features. That may not work if you need the sides to be at an angle to the top face instead of being perpendicular.