I found that the verticle fin on my Avistar was showing the same problems after 1 flight and 2 successive ground runs. So don't be so hard on yourself. It appears to be a weak point in the model and is better to have caught it on the ground than in mid-air. As mentioned, just darefully peel back enough covering to reattach the fin. Reinforce the base area with sime balsa triangle stock. ANd recover the joint. It took me about an hour to do mine and it's been rock solid ever since.