Just 3M fixing tape, and yeah it was hard to get it on right. But it's mainly held on at the top of the plate down to the middle, the bottom isn't really connected to the car. But it doesn't matter and it hasn't moved since I installed it so obviously okay! (have been +100 mph)
I gave the plate a little bend with my hands, not too much as it'll snap and eventually it will conform to the front panel anyway due to the tension and time.