Welcome to the forum!
The Sonic has a decent start for a tapering hatchback spoiler. It was noted around here when they first previewed the production version of the car (back when they were still calling it an Aveo).
The Spark rear spoiler is similar to yours, and they even made a slightly longer one for the electric version of the car to increase efficiency.
Did you get the 1.4t or the 1.8? Manual/auto?
Make a garage entry for your car and start tracking your mileage so we know what's going on.