If the dog is not fitting in to your home and you have issues after 6 months, do not hesitate to return him. There is nothing wrong with not bonding with a dog. Sometimes it takes a while for everyone to realize it is not a good fit.
Your group would rather have him back and work on finding the perfect home for him than have both you and the dog being in a so-so relationship. You can ask to foster another dog for a few weeks before you adopt another one.
Return him with a nice dossier of information about his feeding schedule, likes and habits, some pictures and a few of his favorite toys will help him adjust to the move. It will also help his next family know what kind of dog they are adopting and make the transition go smoothly for everyone.
Make the decision, get everything lined up and call the group and let them know what you want to do. The sooner this happens, the better chance he has of finding another home quickly. Good luck. Remember, it's the dog well-being that is most important here, not what the group or what others think.