Can you give it more power?
Also what you reflect from, smooth metal is best and for testing a corner reflector will send the most back. If you take a box and cut so there are 3 sides together making a corner then line the inside of that with smooth foil (try not to wrinkle) you will have a cheap corner reflector. Make it not small. Even if the reflector is not pointing directly at the source, the geometry will send the waves back. It works with light, it should work with radar.
Last is movement. The object must move relative to the radar either toward or away though sideways can be mixed in.