Marina, have fun and enjoy the mango. Once more: use a euro peeler or y-peeler to remove the mango skin. This will leave the mango inner skin (the tougher sheet encasing the softer mango inside). This inner skin is what shows on the top face of the rose and what is always in an angle.
After peeling the mango, follow the flat seed (mango seeds are always flat). Hold your mango vertically with the stem down. Cut as close as possible to the flat side of the seed, this will give you the 2 bigger pieces. Now, hold your mango flat (against one of the cut sides), and cut as close as possible to the edge side of the seed, this will give you the 2 smaller pieces.
So now, you have 4 pieces. Lay them on your cutting board with the mango inner skin facing up. Process to slice, like in juliene. Keep the slices together and work in order, so you gradually lay the petals in proportion.
On the larger pieces, grab exactly half of the slices and turn them 180 degrees, this way you have all slices with the same angle. It is the same angle of the inner skin you need to follow when laying the rose. I really need to put this on video!
To start, find the smallest slices (from either the big pieces or small pieces), and form the rose center. It is a little hard to flex the mango, often I mush them a little. Keep working your way out, gradually using from smaller to larger slices.
Again, pay attention to the angle of the inner skin. If you see that the rose petals dissapear when you add a petal next to it, it is because the angle was inverted.
You know, taking some florist design workshops help, just make your own style!