This thing needs to be printed large (to gain enough weight for flight) (> 20 cm x 20 cm). You can try to ad weight at the wing tips.

This is an old model. See BoomerangV01 for new (Scaled Z axis to 0.6 for much better flight)

Note; A boomerang can be dangerous for the unattended! Printed over more than 15 cm in diameter it can cause serious harm! ( age 10+)