Hi, Tarinann and GCC, welcome to the forum and congrats on your new baby (you did not tell us its name0. As to your 'problems', I am afraid that you have untenable expectations because of the species and age of parrot you have. First of all, at only 6 months of age, you are dealing with the equivalent of a 4 year old human child so, of course, the baby wants only to play and be with mama and dada. Your CGG is too young to be formally trained. It's still too flighty and its attention span is next to nothing
Not that you should not teach it anything but what you need to teach is not done in a formal session, it's more a 'teach as you go' like you do with a small child, and just co-habiting things like stepping up and down, not nipping hard, no chewing on nails, etc and, most importantly, to eat a healthy and varied fresh food diet.
As to the 'won't stay off the shoulder'... well, my dear, being on its human's shoulder is, pretty much, all GCCs want out of life, and it's not only when they are young -when the need is much more acute- but all their lives. I have a 10 year old female who never bites, never screams and is the sweetest little thing and all she wants to do is cuddle on my chest and give me kisses all day long. I think that maybe you would have been happier with an amazon who are more independent and actually like just perching somewhere watching what is going on -we call them 'perch potatoes precisely because of this. Parrots might be all parrots and share lots of characteristics but each species has its own needs and, when it comes to GCCs, they need more one-on-one time than all other species except cockatoos.
So, please stop trying to train it until it's older and more 'settled down' and give it as much shoulder time as it wants... plenty of time to teach it stuff.