I've done hand launching for years and every plane can be a bit different. I would suggest two things. One, practice hand launching with tall soft grass in front of where you actually let go. I would practice "test glides", if possible, (power off and prop removed) into the tall grass. If the plane heads for the ground, at least it will land on soft grass. Two, try running into the wind with the airplane held a bit lightly in your hand. You should be able to feel the airplane wanting to lift out of your hand. If the plane has a nice level balanced and "flying" feel, as if it is already flying even though you are still holding it, you can probably then give a light shove forward. If the airplane feels like it wants to lift at an upward angle or has a downward feel, don't launch. Stop and do necessary adustments to CG, wing incidence etc. until it "feels" right when you run with it into a light breeze. Be sure to be looking at the plane as you launch it. Be sure the plane is level or even ever so slightly pointed downward so that it is less likely to be pushed into an immediate stall. You want the plane to be gently pushed straight out, with no upward angle. With a little bit of careful running into a light breeze you don't need to thow the plane hardly at all; a gentle shove is all that is required.