This video discusses how to diagnose your throw if it’s wobbling on the release. This is usually due to your wrist ‘breaking’ on the snap instead of keeping your palm facing up. To correct this you can have the disc dropped below horizontal to start and then as you snap, your natural tendency to bring the disc up will have the disc release flat.
Also, I find people have some problems with their forehand when they try to force the throw along a plane different from the one they’re setting up to throw. What I mean by this is that people will have the disc at an angle different than the one they want to throw (ie outside/in but they want to throw a flat flick). This can cause the disc to initially wobble, it takes a lot of power off the throw and it’s more difficult to have your throw go where you want it to. Just make sure to have your throw go along the same plane from the time you start your windup to the time you release the throw and you won’t have this problem.