I nailed a tree on the trail last weekend and did the same. There should be two small pegs at the top corners that go into two small holes in the headlight surround and two small tabs at the bottom corners that go into the notches in the surround that are by the right/left headlight adjustment screws. Sounds like you snapped some of these off. I ddi and just applied Velcro to it and reattached. Could also easily rivet it to the headlight surround and still be able to get to the headlight surround attachment bolts if needed, this is what I will do if Velcro doesn't hold.
-Bikeman